iterable_dataset.py

import copy
import itertools
from collections import Counter
from copy import deepcopy
from dataclasses import dataclass
from itertools import cycle, islice
from typing import Any, Callable, Dict, Iterable, Iterator, List, Optional, Union

import numpy as np
import pyarrow as pa

from .arrow_dataset import DatasetInfoMixin
from .features import Features, Value
from .features.features import FeatureType
from .formatting import PythonFormatter
from .info import DatasetInfo
from .splits import NamedSplit
from .table import table_cast


def _infer_features_from_batch(batch: Dict[str, list], try_features: Optional[Features] = None) -> Features:
    pa_table = pa.Table.from_pydict(batch)
    if try_features is not None:
        try:
            pa_table = table_cast(pa_table, pa.schema(try_features.type))
        except (TypeError, pa.ArrowInvalid, pa.ArrowNotImplementedError):
            pass
    return Features.from_arrow_schema(pa_table.schema)


def _examples_to_batch(examples: List[Dict[str, Any]]) -> Dict[str, list]:
    cols = sorted(examples[0].keys())
    arrays = []
    for col in cols:
        arrays.append([example[col] for example in examples])
    return dict(zip(cols, arrays))


def _batch_to_examples(batch: Dict[str, list]) -> List[Dict[str, Any]]:
    """Convert a batch (dict of examples) to examples list"""
    n_examples = len(batch[next(iter(batch))])
    for i in range(n_examples):
        yield {col: array[i] for col, array in batch.items()}


class _BaseExamplesIterable:
    """Base class for the examples iterable used by an IterableDataset"""

    def __iter__(self):
        """An examples iterable should yield tuples (example_key, example) of type (int/str, dict)"""
        raise NotImplementedError(f"{type(self)} doesn't implement __iter__ yet")

    def shuffle_data_sources(self, generator: np.random.Generator) -> "_BaseExamplesIterable":
        """
        Either shuffle the shards/sources of the dataset, or propagate the shuffling to the underlying iterable.
        If the order of the shards must stay fixed (when using .skip or .take for example), then this method returns self.
        """
        raise NotImplementedError(f"{type(self)} doesn't implement shuffle_data_sources yet")

    def shard_data_sources(self, shard_idx: int) -> "_BaseExamplesIterable":
        """Either keep only the requested shard, or propagate the request to the underlying iterable."""
        raise NotImplementedError(f"{type(self)} doesn't implement shard_data_sources yet")

    @property
    def n_shards(self) -> int:
        raise NotImplementedError(f"{type(self)} doesn't implement n_shards yet")


def _shuffle_kwargs(rng: np.random.Generator, kwargs: dict) -> dict:
    """Return a shuffled copy of the input kwargs"""
    # We must shuffle all the lists, and lists of the same size must have the same shuffling.
    # This way entangled lists of (shard, shard_metadata) are still in the right order.

    # First, let's generate the shuffled indices per list size
    list_sizes = set(len(value) for value in kwargs.values() if isinstance(value, list))
    indices_per_size = {}
    for size in list_sizes:
        indices_per_size[size] = list(range(size))
        rng.shuffle(indices_per_size[size])
    # Now let's copy the kwargs and shuffle the lists based on their sizes
    shuffled_kwargs = dict(kwargs)
    for key, value in shuffled_kwargs.items():
        if isinstance(value, list):
            shuffled_kwargs[key] = [value[i] for i in indices_per_size[len(value)]]
    return shuffled_kwargs


def _shard_kwargs(shard_idx: int, kwargs: dict) -> dict:
    """Return a copy of the input kwargs but with only one shard"""
    # Having lists of different sizes makes sharding ambigious, raise an error in this case
    # until we decide how to define sharding without ambiguity for users
    lists_lengths = {key: len(value) for key, value in kwargs.items() if isinstance(value, list)}
    if len(set(lists_lengths.values())) > 1:
        raise RuntimeError(
            (
                "Sharding is ambiguous for this dataset: "
                + "we found several data sources lists of different lengths, and we don't know over which list we should parallelize:\n"
                + "\n".join(f"\t- key {key} has length {length}" for key, length in lists_lengths.items())
                + "\nTo fix this, check the dataset script 'gen_kwargs' and make sure to use lists only for data sources, "
                + "and use tuples otherwise. In the end there should only be one single list, or several lists with the same length."
            )
        )
    return {key: [value[shard_idx]] if isinstance(value, list) else value for key, value in kwargs.items()}


class ExamplesIterable(_BaseExamplesIterable):
    def __init__(self, generate_examples_fn: Callable, kwargs: dict):
        self.generate_examples_fn = generate_examples_fn
        self.kwargs = kwargs

    def __iter__(self):
        yield from self.generate_examples_fn(**self.kwargs)

    def shuffle_data_sources(self, generator: np.random.Generator) -> "ExamplesIterable":
        return ShardShuffledExamplesIterable(self.generate_examples_fn, self.kwargs, generator)

    def shard_data_sources(self, shard_idx: int) -> "MappedExamplesIterable":
        """Keep only the requested shard."""
        kwargs_with_requested_data_source = _shard_kwargs(shard_idx, self.kwargs)
        yield from self.generate_examples_fn(**kwargs_with_requested_data_source)

    @property
    def n_shards(self) -> int:
        max_length = max((len(value) for value in self.kwargs.values() if isinstance(value, list)), default=0)
        return max(1, max_length)


class ShardShuffledExamplesIterable(ExamplesIterable):
    def __init__(self, generate_examples_fn: Callable, kwargs: dict, generator: np.random.Generator):
        super().__init__(generate_examples_fn, kwargs)
        self.generator = deepcopy(generator)

    def __iter__(self):
        """Shuffle the kwargs order to shuffle shards"""
        rng = deepcopy(self.generator)
        kwargs_with_shuffled_shards = _shuffle_kwargs(rng, self.kwargs)
        yield from self.generate_examples_fn(**kwargs_with_shuffled_shards)

    def shard_data_sources(self, shard_idx: int) -> "MappedExamplesIterable":
        """Keep only the requested shard."""
        rng = deepcopy(self.generator)
        kwargs_with_shuffled_shards = _shuffle_kwargs(rng, self.kwargs)
        kwargs_with_requested_data_source = _shard_kwargs(shard_idx, kwargs_with_shuffled_shards)
        return ExamplesIterable(self.generate_examples_fn, kwargs_with_requested_data_source)


class CyclingMultiSourcesExamplesIterable(_BaseExamplesIterable):
    def __init__(self, ex_iterables: List[_BaseExamplesIterable]):
        self.ex_iterables = ex_iterables

    def __iter__(self):
        iterators = [iter(ex_iterable) for ex_iterable in self.ex_iterables]
        # this is an infinite iterator to keep track of which iterator we want to pick examples from
        indices_iterator = cycle(range(len(iterators)))
        for i in indices_iterator:
            try:  # let's pick one example from the iterator at index i
                yield next(iterators[i])
            except StopIteration:  # if we ran out of examples on this iterator, break the main for loop
                break

    def shuffle_data_sources(self, generator: np.random.Generator) -> "CyclingMultiSourcesExamplesIterable":
        """Shuffle each underlying examples iterable."""
        ex_iterables = [ex_iterable.shuffle_data_sources(generator) for ex_iterable in self.ex_iterables]
        return CyclingMultiSourcesExamplesIterable(ex_iterables)

    @property
    def n_shards(self) -> int:
        return sum(ex_iterable.n_shards for ex_iterable in self.ex_iterables)

    def shard_data_sources(self, shard_idx: int) -> "CyclingMultiSourcesExamplesIterable":
        """Either keep only the requested shard, or propagate the request to the underlying iterable."""
        raise NotImplementedError("Sharding a CyclingMultiSourcesExamplesIterable is not implemented")


class VerticallyConcatenatedMultiSourcesExamplesIterable(_BaseExamplesIterable):
    """
    VerticallyConcatenatedMultiSourcesExamplesIterable simply chains the input iterables.
    It doesn't require the examples iterables to always yield the same columns.
    Instead, this is handled by the `IterableDataset` class or `TypedExamplesIterable`.

    For information, `IterableDataset` merges the features of all the datasets to concatenate into one.
    We use `IterableDataset._resolve_features` to obtain the features of all the datasets to concatenate.

    Then for each example, `IterableDataset` and `TypedExamplesIterable` automatically fill missing columns with None.
    This is done with `_apply_feature_types`.
    """

    def __init__(self, ex_iterables: List[_BaseExamplesIterable]):
        self.ex_iterables = ex_iterables

    def __iter__(self):
        for ex_iterable in self.ex_iterables:
            yield from ex_iterable

    def shuffle_data_sources(
        self, generator: np.random.Generator
    ) -> "VerticallyConcatenatedMultiSourcesExamplesIterable":
        """Shuffle the list of examples iterable, as well as each underlying examples iterable."""
        rng = deepcopy(generator)
        ex_iterables = list(self.ex_iterables)
        rng.shuffle(ex_iterables)
        ex_iterables = [ex_iterable.shuffle_data_sources(generator) for ex_iterable in ex_iterables]
        return VerticallyConcatenatedMultiSourcesExamplesIterable(ex_iterables)

    @property
    def n_shards(self) -> int:
        return sum(ex_iterable.n_shards for ex_iterable in self.ex_iterables)

    def shard_data_sources(self, shard_idx: int) -> "VerticallyConcatenatedMultiSourcesExamplesIterable":
        """Either keep only the requested shard, or propagate the request to the underlying iterable."""
        raise NotImplementedError("Sharding a VerticallyConcatenatedMultiSourcesExamplesIterable is not implemented")


def _check_column_names(column_names: List[str]):
    """Check the column names to make sure they don't contain duplicates."""
    counter = Counter(column_names)
    if not all(count == 1 for count in counter.values()):
        duplicated_columns = [col for col in counter if counter[col] > 1]
        raise ValueError(
            f"The examples iterables can't have duplicated columns but columns {duplicated_columns} are duplicated."
        )


class HorizontallyConcatenatedMultiSourcesExamplesIterable(_BaseExamplesIterable):
    """
    HorizontallyConcatenatedMultiSourcesExamplesIterable merges examples together for the input list of iterables.
    It also checks that there are no duplicate columns (otherwise we don't know which one to keep).
    This check is done once when yielding the first example.

    However it doesn't fill missing columns with None.
    Instead, this is handled by the `IterableDataset` class or `TypedExamplesIterable`.

    For information, `IterableDataset` merges the features of all the datasets to concatenate into one.
    We use `IterableDataset._resolve_features` to obtain the features of all the datasets to concatenate.

    Then for each example, `IterableDataset` and `TypedExamplesIterable` automatically fill missing columns with None.
    This is done with `_apply_feature_types`.
    """

    def __init__(self, ex_iterables: List[_BaseExamplesIterable]):
        self.ex_iterables = ex_iterables

    def __iter__(self):
        ex_iterators = [iter(ex_iterable) for ex_iterable in self.ex_iterables]
        for i in itertools.count():
            keys = []
            examples = []
            for ex_iterator in list(ex_iterators):
                try:
                    key, example = next(ex_iterator)
                    keys.append(key)
                    examples.append(example)
                except StopIteration:
                    ex_iterators.remove(ex_iterator)
            if ex_iterators:
                if i == 0:
                    _check_column_names([column_name for example in examples for column_name in example])
                new_example = {}
                for example in examples:
                    new_example.update(example)
                new_key = "_".join(str(key) for key in keys)
                yield new_key, new_example
            else:
                break

    def shuffle_data_sources(
        self, generator: np.random.Generator
    ) -> "HorizontallyConcatenatedMultiSourcesExamplesIterable":
        """Doesn't shuffle the wrapped examples iterable since it would break the alignment between them."""
        return self

    @property
    def n_shards(self) -> int:
        return 1

    def shard_data_sources(self, shard_idx: int) -> "HorizontallyConcatenatedMultiSourcesExamplesIterable":
        """Either keep only the requested shard, or propagate the request to the underlying iterable."""
        raise NotImplementedError("Sharding a HorizontallyConcatenatedMultiSourcesExamplesIterable is not implemented")


class RandomlyCyclingMultiSourcesExamplesIterable(CyclingMultiSourcesExamplesIterable):
    def __init__(self, ex_iterables, generator: np.random.Generator, probabilities: Optional[List[float]] = None):
        super().__init__(ex_iterables)
        self.generator = deepcopy(generator)
        self.probabilities = probabilities

    @staticmethod
    def _iter_random_indices(
        rng: np.random.Generator,
        num_sources: int,
        random_batch_size=1000,
        p: Optional[List[float]] = None,
    ) -> Iterator[int]:
        """Get an infinite iterator that randomly samples the index of the source to pick examples from."""
        if p is None:
            while True:
                yield from (int(i) for i in rng.integers(0, num_sources, size=random_batch_size))
        else:
            while True:
                yield from (int(i) for i in rng.choice(num_sources, size=random_batch_size, p=p))

    def __iter__(self):
        rng = deepcopy(self.generator)
        iterators = [iter(ex_iterable) for ex_iterable in self.ex_iterables]
        # this is an infinite iterator that randomly samples the index of the source to pick examples from
        indices_iterator = self._iter_random_indices(rng, len(iterators), p=self.probabilities)
        for i in indices_iterator:
            try:  # let's pick one example from the iterator at index i
                yield next(iterators[i])
            except StopIteration:  # if we ran out of examples on this iterator, break the main for loop
                break

    def shuffle_data_sources(self, generator: np.random.Generator) -> "RandomlyCyclingMultiSourcesExamplesIterable":
        """Shuffle the data sources of each wrapped examples iterable."""
        ex_iterables = [ex_iterable.shuffle_data_sources(generator) for ex_iterable in self.ex_iterables]
        return RandomlyCyclingMultiSourcesExamplesIterable(
            ex_iterables, generator=generator, probabilities=self.probabilities
        )

    def shard_data_sources(self, shard_idx: int) -> "RandomlyCyclingMultiSourcesExamplesIterable":
        """Either keep only the requested shard, or propagate the request to the underlying iterable."""
        raise NotImplementedError("Sharding a RandomlyCyclingMultiSourcesExamplesIterable is not implemented")


class MappedExamplesIterable(_BaseExamplesIterable):
    def __init__(
        self,
        ex_iterable: _BaseExamplesIterable,
        function: Callable,
        with_indices: bool = False,
        input_columns: Optional[List[str]] = None,
        batched: bool = False,
        batch_size: int = 1000,
        drop_last_batch: bool = False,
        remove_columns: Optional[List[str]] = None,
    ):
        self.ex_iterable = ex_iterable
        self.function = function
        self.batched = batched
        self.batch_size = batch_size
        self.drop_last_batch = drop_last_batch
        self.remove_columns = remove_columns
        self.with_indices = with_indices
        self.input_columns = input_columns

    def __iter__(self):
        iterator = iter(self.ex_iterable)
        current_idx = 0
        if self.batched:
            for key, example in iterator:
                # If batched, first build the batch
                key_examples_list = [(key, example)] + [
                    (key, example) for key, example in islice(iterator, self.batch_size - 1)
                ]
                keys, examples = zip(*key_examples_list)
                if self.drop_last_batch and len(examples) < self.batch_size:  # ignore last batch
                    return
                batch = _examples_to_batch(examples)
                # then apply the transform
                inputs = batch
                function_args = [inputs] if self.input_columns is None else [inputs[col] for col in self.input_columns]
                if self.with_indices:
                    function_args.append([current_idx + i for i in range(len(key_examples_list))])
                transformed_batch = dict(batch)  # this will be updated with the function output
                transformed_batch.update(self.function(*function_args))
                # then remove the unwanted columns
                if self.remove_columns:
                    for c in self.remove_columns:
                        del transformed_batch[c]
                if transformed_batch:
                    first_col = next(iter(transformed_batch))
                    bad_cols = [
                        col
                        for col in transformed_batch
                        if len(transformed_batch[col]) != len(transformed_batch[first_col])
                    ]
                    if bad_cols:
                        raise ValueError(
                            f"Column lengths mismatch: columns {bad_cols} have length {[len(transformed_batch[col]) for col in bad_cols]} while {first_col} has length {len(transformed_batch[first_col])}."
                        )
                # the new key is the concatenation of the examples keys from the batch
                new_key = "_".join(str(key) for key in keys)
                # yield one example at a time from the transformed batch
                for batch_idx, example in enumerate(_batch_to_examples(transformed_batch)):
                    yield new_key, example
                current_idx += batch_idx + 1
        else:
            for key, example in iterator:
                # If not batched, we can apply the transform and yield the example directly
                # first copy the example, since we might drop some keys
                example = dict(example)
                # then apply the transform
                inputs = example
                function_args = [inputs] if self.input_columns is None else [inputs[col] for col in self.input_columns]
                if self.with_indices:
                    function_args.append(current_idx)
                transformed_example = dict(example)  # this will be updated with the function output
                transformed_example.update(self.function(*function_args))
                # then we remove the unwanted columns
                if self.remove_columns:
                    for c in self.remove_columns:
                        del transformed_example[c]
                yield key, transformed_example
                current_idx += 1

    def shuffle_data_sources(self, generator: np.random.Generator) -> "MappedExamplesIterable":
        """Shuffle the wrapped examples iterable."""
        return MappedExamplesIterable(
            self.ex_iterable.shuffle_data_sources(generator),
            function=self.function,
            with_indices=self.with_indices,
            input_columns=self.input_columns,
            batched=self.batched,
            batch_size=self.batch_size,
            remove_columns=self.remove_columns,
        )

    def shard_data_sources(self, shard_idx: int) -> "MappedExamplesIterable":
        """Keep only the requested shard."""
        return MappedExamplesIterable(
            self.ex_iterable.shard_data_sources(shard_idx),
            function=self.function,
            with_indices=self.with_indices,
            input_columns=self.input_columns,
            batched=self.batched,
            batch_size=self.batch_size,
            remove_columns=self.remove_columns,
        )

    @property
    def n_shards(self) -> int:
        return self.ex_iterable.n_shards


class FilteredExamplesIterable(_BaseExamplesIterable):
    def __init__(
        self,
        ex_iterable: _BaseExamplesIterable,
        function: Callable,
        with_indices: bool = False,
        input_columns: Optional[List[str]] = None,
        batched: bool = False,
        batch_size: int = 1000,
    ):
        self.ex_iterable = ex_iterable
        self.function = function
        self.batched = batched
        self.batch_size = batch_size
        self.with_indices = with_indices
        self.input_columns = input_columns

    def __iter__(self):
        iterator = iter(self.ex_iterable)
        current_idx = 0
        if self.batched:
            for key, example in iterator:
                # If batched, first build the batch
                key_examples_list = [(key, example)] + [
                    (key, example) for key, example in islice(iterator, self.batch_size - 1)
                ]
                keys, examples = zip(*key_examples_list)
                batch = _examples_to_batch(examples)
                # then compute the mask for the batch
                inputs = batch
                function_args = [inputs] if self.input_columns is None else [inputs[col] for col in self.input_columns]
                if self.with_indices:
                    function_args.append([current_idx + i for i in range(len(key_examples_list))])
                mask = self.function(*function_args)
                # yield one example at a time from the batch
                for batch_idx, (key_example, to_keep) in enumerate(zip(key_examples_list, mask)):
                    if to_keep:
                        yield key_example
                current_idx += batch_idx + 1
        else:
            for key, example in iterator:
                # If not batched, we can apply the filtering function direcly
                inputs = dict(example)
                function_args = [inputs] if self.input_columns is None else [inputs[col] for col in self.input_columns]
                if self.with_indices:
                    function_args.append(current_idx)
                to_keep = self.function(*function_args)
                if to_keep:
                    yield key, example
                current_idx += 1

    def shuffle_data_sources(self, seed: Optional[int]) -> "FilteredExamplesIterable":
        """Shuffle the wrapped examples iterable."""
        return FilteredExamplesIterable(
            self.ex_iterable.shuffle_data_sources(seed),
            function=self.function,
            with_indices=self.with_indices,
            input_columns=self.input_columns,
            batched=self.batched,
            batch_size=self.batch_size,
        )

    def shard_data_sources(self, shard_idx: int) -> "FilteredExamplesIterable":
        """Keep only the requested shard."""
        return FilteredExamplesIterable(
            self.ex_iterable.shard_data_sources(shard_idx),
            function=self.function,
            with_indices=self.with_indices,
            input_columns=self.input_columns,
            batched=self.batched,
            batch_size=self.batch_size,
        )

    @property
    def n_shards(self) -> int:
        return self.ex_iterable.n_shards


class BufferShuffledExamplesIterable(_BaseExamplesIterable):
    def __init__(self, ex_iterable: _BaseExamplesIterable, buffer_size: int, generator: np.random.Generator):
        self.ex_iterable = ex_iterable
        self.buffer_size = buffer_size
        self.generator = generator

    @staticmethod
    def _iter_random_indices(rng: np.random.Generator, buffer_size: int, random_batch_size=1000) -> Iterator[int]:
        while True:
            yield from (int(i) for i in rng.integers(0, buffer_size, size=random_batch_size))

    def __iter__(self):
        buffer_size = self.buffer_size
        rng = deepcopy(self.generator)
        indices_iterator = self._iter_random_indices(rng, buffer_size)
        # this is the shuffle buffer that we keep in memory
        mem_buffer = []
        for x in self.ex_iterable:
            if len(mem_buffer) == buffer_size:  # if the buffer is full, pick and example from it
                i = next(indices_iterator)
                yield mem_buffer[i]
                mem_buffer[i] = x  # replace the picked example by a new one
            else:  # otherwise, keep filling the buffer
                mem_buffer.append(x)
        # when we run out of examples, we shuffle the remaining examples in the buffer and yield them
        rng.shuffle(mem_buffer)
        yield from mem_buffer

    def shuffle_data_sources(self, generator: np.random.Generator) -> "BufferShuffledExamplesIterable":
        """Shuffle the wrapped examples iterable as well as the shuffling buffer."""
        return BufferShuffledExamplesIterable(
            self.ex_iterable.shuffle_data_sources(generator), buffer_size=self.buffer_size, generator=generator
        )

    def shard_data_sources(self, shard_idx: int) -> "BufferShuffledExamplesIterable":
        """Keep only the requested shard."""
        return BufferShuffledExamplesIterable(
            self.ex_iterable.shard_data_sources(shard_idx), buffer_size=self.buffer_size, generator=self.generator
        )

    @property
    def n_shards(self) -> int:
        return self.ex_iterable.n_shards


class SkipExamplesIterable(_BaseExamplesIterable):
    def __init__(self, ex_iterable: _BaseExamplesIterable, n: int):
        self.ex_iterable = ex_iterable
        self.n = n

    def __iter__(self):
        ex_iterator = iter(self.ex_iterable)
        for _ in islice(ex_iterator, self.n):
            pass
        yield from ex_iterator

    def shuffle_data_sources(self, generator: np.random.Generator) -> "SkipExamplesIterable":
        """Doesn't shuffle the wrapped examples iterable since it would skip examples from other shards instead."""
        return self

    @property
    def n_shards(self) -> int:
        return self.ex_iterable.n_shards


class TakeExamplesIterable(_BaseExamplesIterable):
    def __init__(self, ex_iterable: _BaseExamplesIterable, n: int):
        self.ex_iterable = ex_iterable
        self.n = n

    def __iter__(self):
        yield from islice(self.ex_iterable, self.n)

    def shuffle_data_sources(self, generator: np.random.Generator) -> "TakeExamplesIterable":
        """Doesn't shuffle the wrapped examples iterable since it would take examples from other shards instead."""
        return self

    @property
    def n_shards(self) -> int:
        return self.ex_iterable.n_shards


def _apply_feature_types(
    example: dict, features: Features, token_per_repo_id: Dict[str, Union[str, bool, None]]
) -> dict:
    example = dict(example)
    # add missing columns
    for column_name in features:
        if column_name not in example:
            example[column_name] = None
    # we encode the example for ClassLabel feature types for example
    encoded_example = features.encode_example(example)
    # Decode example for Audio feature, e.g.
    decoded_example = features.decode_example(encoded_example, token_per_repo_id=token_per_repo_id)
    return decoded_example


class TypedExamplesIterable(_BaseExamplesIterable):
    def __init__(
        self,
        ex_iterable: _BaseExamplesIterable,
        features: Features,
        token_per_repo_id: Dict[str, Union[str, bool, None]],
    ):
        self.ex_iterable = ex_iterable
        self.features = features
        self.token_per_repo_id = token_per_repo_id

    def __iter__(self):
        # Then for each example, `TypedExamplesIterable` automatically fills missing columns with None.
        # This is done with `_apply_feature_types`.
        for key, example in self.ex_iterable:
            yield key, _apply_feature_types(example, self.features, token_per_repo_id=self.token_per_repo_id)

    def shuffle_data_sources(self, generator: np.random.Generator) -> "TypedExamplesIterable":
        """Shuffle the wrapped examples iterable."""
        return TypedExamplesIterable(
            self.ex_iterable.shuffle_data_sources(generator),
            features=self.features,
            token_per_repo_id=self.token_per_repo_id,
        )

    def shard_data_sources(self, shard_idx: int) -> "TypedExamplesIterable":
        """Keep only the requested shard."""
        return TypedExamplesIterable(
            self.ex_iterable.shard_data_sources(shard_idx),
            features=self.features,
            token_per_repo_id=self.token_per_repo_id,
        )

    @property
    def n_shards(self) -> int:
        return self.ex_iterable.n_shards


def _generate_examples_from_tables_wrapper(generate_tables_fn):
    def wrapper(**kwargs):
        python_formatter = PythonFormatter()
        for key, table in generate_tables_fn(**kwargs):
            batch = python_formatter.format_batch(table)
            for i, example in enumerate(_batch_to_examples(batch)):
                yield f"{key}_{i}", example

    return wrapper


@dataclass
class ShufflingConfig:
    generator: np.random.Generator


class IterableDataset(DatasetInfoMixin):
    """A Dataset backed by an iterable."""

    def __init__(
        self,
        ex_iterable: _BaseExamplesIterable,
        info: Optional[DatasetInfo] = None,
        split: Optional[NamedSplit] = None,
        format_type: Optional[str] = None,
        shuffling: Optional[ShufflingConfig] = None,
        token_per_repo_id: Optional[Dict[str, Union[str, bool, None]]] = None,
    ):
        info = info.copy() if info is not None else DatasetInfo()
        DatasetInfoMixin.__init__(self, info=info, split=split)

        self._ex_iterable = ex_iterable
        self._format_type = format_type
        self._shuffling = shuffling
        self._epoch = 0
        self._token_per_repo_id: Dict[str, Union[str, bool, None]] = token_per_repo_id or {}

    def _head(self, n=5):
        return _examples_to_batch([x for key, x in islice(self._iter(), n)])

    def _effective_generator(self):
        if self._shuffling and self._epoch == 0:
            return self._shuffling.generator
        elif self._shuffling:
            # Create effective seed using self._epoch (we subtract in order to avoir overflow in long_scalars)
            effective_seed = deepcopy(self._shuffling.generator).integers(0, 1 << 63) - self._epoch
            effective_seed = (1 << 63) + effective_seed if effective_seed < 0 else effective_seed
            return np.random.default_rng(effective_seed)
        else:
            raise ValueError("This dataset is not shuffled")

    @property
    def n_shards(self) -> int:
        return self._ex_iterable.n_shards

    def _iter(self):
        if self._shuffling:
            ex_iterable = self._ex_iterable.shuffle_data_sources(self._effective_generator())
        else:
            ex_iterable = self._ex_iterable
        yield from ex_iterable

    def _iter_shard(self, shard_idx: int):
        if self._shuffling:
            ex_iterable = self._ex_iterable.shuffle_data_sources(self._effective_generator())
        else:
            ex_iterable = self._ex_iterable
        yield from ex_iterable.shard_data_sources(shard_idx)

    def __iter__(self):
        for key, example in self._iter():
            if self.features:
                # `IterableDataset` automatically fills missing columns with None.
                # This is done with `_apply_feature_types`.
                yield _apply_feature_types(example, self.features, token_per_repo_id=self._token_per_repo_id)
            else:
                yield example

    def with_format(
        self,
        type: Optional[str] = None,
    ) -> "IterableDataset":
        """
        Return a dataset with the specified format.
        This method only supports the "torch" format for now.

        Args:

            type (:obj:`str`, optional, default None): if set to "torch", the returned dataset
                will be a subclass of torch.utils.data.IterableDataset to be used in a DataLoader
        """
        # TODO(QL): add examples formatting to get tensors when using the "torch" format
        # TODO(QL): add format_kwargs
        # TODO(QL): add format_columns and return_all_columns
        # TODO(QL): add pandas, numpy and tf formats
        return iterable_dataset(
            ex_iterable=self._ex_iterable,
            info=self._info.copy(),
            split=self._split,
            format_type=type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def map(
        self,
        function: Optional[Callable] = None,
        with_indices: bool = False,
        input_columns: Optional[Union[str, List[str]]] = None,
        batched: bool = False,
        batch_size: int = 1000,
        drop_last_batch: bool = False,
        remove_columns: Optional[Union[str, List[str]]] = None,
    ) -> "IterableDataset":
        """
        Apply a function to all the examples in the iterable dataset (individually or in batches) and update them.
        If your function returns a column that already exists, then it overwrites it.
        The function is applied on-the-fly on the examples when iterating over the dataset.

        You can specify whether the function should be batched or not with the ``batched`` parameter:

        - If batched is False, then the function takes 1 example in and should return 1 example.
          An example is a dictionary, e.g. {"text": "Hello there !"}
        - If batched is True and batch_size is 1, then the function takes a batch of 1 example as input and can return a batch with 1 or more examples.
          A batch is a dictionary, e.g. a batch of 1 example is {"text": ["Hello there !"]}
        - If batched is True and batch_size is ``n`` > 1, then the function takes a batch of ``n`` examples as input and can return a batch with ``n`` examples, or with an arbitrary number of examples.
          Note that the last batch may have less than ``n`` examples.
          A batch is a dictionary, e.g. a batch of ``n`` examples is {"text": ["Hello there !"] * n}

        Args:
            function (:obj:`Callable`, optional, default None): Function applied on-the-fly on the examples when you iterate on the dataset
                It must have one of the following signatures:

                - `function(example: Dict[str, Any]) -> Dict[str, Any]` if `batched=False` and `with_indices=False`
                - `function(example: Dict[str, Any], idx: int) -> Dict[str, Any]` if `batched=False` and `with_indices=True`
                - `function(batch: Dict[str, List]) -> Dict[str, List]` if `batched=True` and `with_indices=False`
                - `function(batch: Dict[str, List], indices: List[int]) -> Dict[str, List]` if `batched=True` and `with_indices=True`

                For advanced usage, the function can also return a `pyarrow.Table`.
                Moreover if your function returns nothing (`None`), then `map` will run your function and return the dataset unchanged.
                If no function is provided, default to identity function: ``lambda x: x``.
            with_indices (:obj:`bool`, defaults to `False`): Provide example indices to `function`. Note that in this case the signature of `function` should be `def function(example, idx[, rank]): ...`.
            input_columns (`Optional[Union[str, List[str]]]`, default `None`): The columns to be passed into `function`
                as positional arguments. If `None`, a dict mapping to all formatted columns is passed as one argument.
            batched (:obj:`bool`, default `False`): Provide batch of examples to `function`.
            batch_size (:obj:`int`, optional, default ``1000``): Number of examples per batch provided to `function` if `batched=True`.
            drop_last_batch (:obj:`bool`, default `False`): Whether a last batch smaller than the batch_size should be
                dropped instead of being processed by the function.
            remove_columns (`Optional[List[str]]`, defaults to `None`): Remove a selection of columns while doing the mapping.
                Columns will be removed before updating the examples with the output of `function`, i.e. if `function` is adding
                columns with names in `remove_columns`, these columns will be kept.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> def add_prefix(example):
        ...     example["text"] = "Review: " + example["text"]
        ...     return example
        >>> ds = ds.map(add_prefix)
        >>> list(ds.take(3))
        [{'label': 1,
         'text': 'Review: the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'},
         {'label': 1,
         'text': 'Review: the gorgeously elaborate continuation of " the lord of the rings " trilogy is so huge that a column of words cannot adequately describe co-writer/director peter jackson\'s expanded vision of j . r . r . tolkien\'s middle-earth .'},
         {'label': 1, 'text': 'Review: effective but too-tepid biopic'}]
        ```
        """
        if isinstance(input_columns, str):
            input_columns = [input_columns]
        if isinstance(remove_columns, str):
            remove_columns = [remove_columns]
        if function is None:
            function = lambda x: x  # noqa: E731
        info = self._info.copy()
        info.features = None
        ex_iterable = MappedExamplesIterable(
            TypedExamplesIterable(self._ex_iterable, self._info.features, token_per_repo_id=self._token_per_repo_id)
            if self._info.features is not None
            else self._ex_iterable,
            function=function,
            with_indices=with_indices,
            input_columns=input_columns,
            batched=batched,
            batch_size=batch_size,
            drop_last_batch=drop_last_batch,
            remove_columns=remove_columns,
        )
        return iterable_dataset(
            ex_iterable=ex_iterable,
            info=info,
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def filter(
        self,
        function: Optional[Callable] = None,
        with_indices=False,
        input_columns: Optional[Union[str, List[str]]] = None,
        batched: bool = False,
        batch_size: Optional[int] = 1000,
    ) -> "IterableDataset":
        """Apply a filter function to all the elements so that the dataset only includes examples according to the filter function.
        The filtering is done on-the-fly when iterating over the dataset.

        Args:
            function (:obj:`Callable`): Callable with one of the following signatures:

                - ``function(example: Dict[str, Any]) -> bool`` if ``with_indices=False, batched=False``
                - ``function(example: Dict[str, Any], indices: int) -> bool`` if ``with_indices=True, batched=False``
                - ``function(example: Dict[str, List]) -> List[bool]`` if ``with_indices=False, batched=True``
                - ``function(example: Dict[str, List], indices: List[int]) -> List[bool]`` if ``with_indices=True, batched=True``

                If no function is provided, defaults to an always True function: ``lambda x: True``.
            with_indices (:obj:`bool`, default `False`): Provide example indices to `function`. Note that in this case the signature of `function` should be `def function(example, idx): ...`.
            input_columns (:obj:`str` or `List[str]`, optional): The columns to be passed into `function` as
                positional arguments. If `None`, a dict mapping to all formatted columns is passed as one argument.
            batched (:obj:`bool`, defaults to `False`): Provide batch of examples to `function`
            batch_size (:obj:`int`, optional, default ``1000``): Number of examples per batch provided to `function` if `batched=True`.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> ds = ds.filter(lambda x: x["label"] == 0)
        >>> list(ds.take(3))
        [{'label': 0, 'movie_review': 'simplistic , silly and tedious .'},
         {'label': 0,
         'movie_review': "it's so laddish and juvenile , only teenage boys could possibly find it funny ."},
         {'label': 0,
         'movie_review': 'exploitative and largely devoid of the depth or sophistication that would make watching such a graphic treatment of the crimes bearable .'}]
        ```
        """
        if isinstance(input_columns, str):
            input_columns = [input_columns]

        # TODO(QL): keep the features (right now if we keep it it would call decode_example again on an already decoded example)
        info = copy.deepcopy(self._info)
        info.features = None

        # We need the examples to be decoded for certain feature types like Image or Audio, so we use TypedExamplesIterable here
        ex_iterable = FilteredExamplesIterable(
            TypedExamplesIterable(self._ex_iterable, self._info.features, token_per_repo_id=self._token_per_repo_id)
            if self._info.features is not None
            else self._ex_iterable,
            function=function,
            with_indices=with_indices,
            input_columns=input_columns,
            batched=batched,
            batch_size=batch_size,
        )
        return iterable_dataset(
            ex_iterable=ex_iterable,
            info=info,
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def shuffle(
        self, seed=None, generator: Optional[np.random.Generator] = None, buffer_size: int = 1000
    ) -> "IterableDataset":
        """
        Randomly shuffles the elements of this dataset.

        This dataset fills a buffer with buffer_size elements, then randomly samples elements from this buffer,
        replacing the selected elements with new elements. For perfect shuffling, a buffer size greater than or
        equal to the full size of the dataset is required.

        For instance, if your dataset contains 10,000 elements but ``buffer_size`` is set to 1,000, then shuffle will
        initially select a random element from only the first 1,000 elements in the buffer. Once an element is
        selected, its space in the buffer is replaced by the next (i.e. 1,001-st) element,
        maintaining the 1,000 element buffer.

        If the dataset is made of several shards, it also does shuffle the order of the shards.
        However if the order has been fixed by using :func:`datasets.IterableDataset.skip` or :func:`datasets.IterableDataset.take`
        then the order of the shards is kept unchanged.

        Args:
            seed (:obj:`int`, optional, default None): random seed that will be used to shuffle the dataset.
                It is used to sample from the shuffle buffe and als oto shuffle the data shards.
            generator (:obj:`numpy.random.Generator`, optional): Numpy random Generator to use to compute the permutation of the dataset rows.
                If ``generator=None`` (default), uses np.random.default_rng (the default BitGenerator (PCG64) of NumPy).
            buffer_size (:obj:`int`, default 1000): size of the buffer.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> list(ds.take(3))
        [{'label': 1,
         'text': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'},
         {'label': 1,
         'text': 'the gorgeously elaborate continuation of " the lord of the rings " trilogy is so huge that a column of words cannot adequately describe co-writer/director peter jackson\'s expanded vision of j . r . r . tolkien\'s middle-earth .'},
         {'label': 1, 'text': 'effective but too-tepid biopic'}]
        >>> shuffled_ds = ds.shuffle(seed=42)
        >>> list(shuffled_ds.take(3))
        [{'label': 1,
         'text': "a sports movie with action that's exciting on the field and a story you care about off it ."},
         {'label': 1,
         'text': 'at its best , the good girl is a refreshingly adult take on adultery . . .'},
         {'label': 1,
         'text': "sam jones became a very lucky filmmaker the day wilco got dropped from their record label , proving that one man's ruin may be another's fortune ."}]
        ```
        """
        if generator is None:
            generator = np.random.default_rng(seed)
        else:
            generator = deepcopy(generator)
        shuffling = ShufflingConfig(generator=generator)
        return iterable_dataset(
            ex_iterable=BufferShuffledExamplesIterable(
                self._ex_iterable, buffer_size=buffer_size, generator=generator
            ).shuffle_data_sources(generator),
            info=self._info.copy(),
            split=self._split,
            format_type=self._format_type,
            shuffling=shuffling,
            token_per_repo_id=self._token_per_repo_id,
        )

    def set_epoch(self, epoch: int):
        self._epoch = epoch

    def skip(self, n) -> "IterableDataset":
        """
        Create a new IterableDataset that skips the first ``n`` elements.

        Args:
            n (:obj:`int`): number of elements to skip.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> list(ds.take(3))
        [{'label': 1,
         'text': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'},
         {'label': 1,
         'text': 'the gorgeously elaborate continuation of " the lord of the rings " trilogy is so huge that a column of words cannot adequately describe co-writer/director peter jackson\'s expanded vision of j . r . r . tolkien\'s middle-earth .'},
         {'label': 1, 'text': 'effective but too-tepid biopic'}]
        >>> ds = ds.skip(1)
        >>> list(ds.take(3))
        [{'label': 1,
         'text': 'the gorgeously elaborate continuation of " the lord of the rings " trilogy is so huge that a column of words cannot adequately describe co-writer/director peter jackson\'s expanded vision of j . r . r . tolkien\'s middle-earth .'},
         {'label': 1, 'text': 'effective but too-tepid biopic'},
         {'label': 1,
         'text': 'if you sometimes like to go to the movies to have fun , wasabi is a good place to start .'}]
        ```
        """
        ex_iterable = SkipExamplesIterable(self._ex_iterable, n)
        return iterable_dataset(
            ex_iterable=ex_iterable,
            info=self._info.copy(),
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def take(self, n) -> "IterableDataset":
        """
        Create a new IterableDataset with only the first ``n`` elements.

        Args:
            n (:obj:`int`): number of elements to take.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> small_ds = ds.take(2)
        >>> list(small_ds)
        [{'label': 1,
         'text': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'},
         {'label': 1,
         'text': 'the gorgeously elaborate continuation of " the lord of the rings " trilogy is so huge that a column of words cannot adequately describe co-writer/director peter jackson\'s expanded vision of j . r . r . tolkien\'s middle-earth .'}]
        ```
        """
        ex_iterable = TakeExamplesIterable(self._ex_iterable, n)
        return iterable_dataset(
            ex_iterable=ex_iterable,
            info=self._info.copy(),
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def add_column(self, name: str, column: Union[list, np.array]) -> "IterableDataset":
        """Add column to Dataset.

        Args:
            name (str): Column name.
            column (list or np.array): Column data to be added.

        Returns:
            :class:`IterableDataset`
        """

        def add_column_fn(example, idx):
            if name in example:
                raise ValueError(f"Error when adding {name}: column {name} is already in the dataset.")
            return {name: column[idx]}

        return self.map(add_column_fn, with_indices=True)

    def rename_column(self, original_column_name: str, new_column_name: str) -> "IterableDataset":
        """
        Rename a column in the dataset, and move the features associated to the original column under the new column
        name.

        Args:
            original_column_name (:obj:`str`): Name of the column to rename.
            new_column_name (:obj:`str`): New name for the column.

        Returns:
            :class:`IterableDataset`: A copy of the dataset with a renamed column.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> next(iter(ds))
        {'label': 1,
         'text': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'}
        >>> ds.rename_column("text", "movie_review")
        >>> next(iter(ds))
        {'label': 1,
         'movie_review': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'}
        ```
        """

        def rename_column_fn(example):
            if original_column_name not in example:
                raise ValueError(
                    f"Error when renaming {original_column_name} to {new_column_name}: column {original_column_name} is not in the dataset."
                )
            if new_column_name in example:
                raise ValueError(
                    f"Error when renaming {original_column_name} to {new_column_name}: column {new_column_name} is already in the dataset."
                )
            return {new_column_name: example[original_column_name]}

        return self.map(rename_column_fn, remove_columns=[original_column_name])

    def rename_columns(self, column_mapping: Dict[str, str]) -> "IterableDataset":
        """
        Rename several columns in the dataset, and move the features associated to the original columns under
        the new column names.

        Args:
            column_mapping (:obj:`Dict[str, str]`): A mapping of columns to rename to their new names

        Returns:
            :class:`IterableDataset`: A copy of the dataset with renamed columns
        """

        def rename_columns_fn(example):
            if any(col not in example for col in column_mapping):
                raise ValueError(
                    f"Error when renaming {list(column_mapping)} to {list(column_mapping.values())}: columns {set(column_mapping) - set(example)} are not in the dataset."
                )
            if any(col in example for col in column_mapping.values()):
                raise ValueError(
                    f"Error when renaming {list(column_mapping)} to {list(column_mapping.values())}: columns {set(example) - set(column_mapping.values())} are already in the dataset."
                )
            return {
                new_column_name: example[original_column_name]
                for original_column_name, new_column_name in column_mapping.items()
            }

        return self.map(rename_columns_fn, remove_columns=list(column_mapping))

    def remove_columns(self, column_names: Union[str, List[str]]) -> "IterableDataset":
        """
        Remove one or several column(s) in the dataset and the features associated to them.
        The removal is done on-the-fly on the examples when iterating over the dataset.


        Args:
            column_names (:obj:`Union[str, List[str]]`): Name of the column(s) to remove.

        Returns:
            :class:`IterableDataset`: A copy of the dataset object without the columns to remove.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> next(iter(ds))
        {'text': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .', 'label': 1}
        >>> ds = ds.remove_columns("label")
        >>> next(iter(ds))
        {'text': 'the rock is destined to be the 21st century\'s new " conan " and that he\'s going to make a splash even greater than arnold schwarzenegger , jean-claud van damme or steven segal .'}
        ```
        """
        return self.map(remove_columns=column_names)

    def cast_column(self, column: str, feature: FeatureType) -> "IterableDataset":
        """Cast column to feature for decoding.

        Args:
            column (:obj:`str`): Column name.
            feature (:class:`Feature`): Target feature.

        Returns:
            :class:`IterableDataset`

        Example:

        ```py
        >>> from datasets import load_dataset, Audio
        >>> ds = load_dataset("PolyAI/minds14", name="en-US", split="train", streaming=True)
        >>> ds.features
        {'audio': Audio(sampling_rate=8000, mono=True, decode=True, id=None),
         'english_transcription': Value(dtype='string', id=None),
         'intent_class': ClassLabel(num_classes=14, names=['abroad', 'address', 'app_error', 'atm_limit', 'balance', 'business_loan',  'card_issues', 'cash_deposit', 'direct_debit', 'freeze', 'high_value_payment', 'joint_account', 'latest_transactions', 'pay_bill'], id=None),
         'lang_id': ClassLabel(num_classes=14, names=['cs-CZ', 'de-DE', 'en-AU', 'en-GB', 'en-US', 'es-ES', 'fr-FR', 'it-IT', 'ko-KR',  'nl-NL', 'pl-PL', 'pt-PT', 'ru-RU', 'zh-CN'], id=None),
         'path': Value(dtype='string', id=None),
         'transcription': Value(dtype='string', id=None)}
        >>> ds = ds.cast_column("audio", Audio(sampling_rate=16000))
        >>> ds.features
        {'audio': Audio(sampling_rate=16000, mono=True, decode=True, id=None),
         'english_transcription': Value(dtype='string', id=None),
         'intent_class': ClassLabel(num_classes=14, names=['abroad', 'address', 'app_error', 'atm_limit', 'balance', 'business_loan',  'card_issues', 'cash_deposit', 'direct_debit', 'freeze', 'high_value_payment', 'joint_account', 'latest_transactions', 'pay_bill'], id=None),
         'lang_id': ClassLabel(num_classes=14, names=['cs-CZ', 'de-DE', 'en-AU', 'en-GB', 'en-US', 'es-ES', 'fr-FR', 'it-IT', 'ko-KR',  'nl-NL', 'pl-PL', 'pt-PT', 'ru-RU', 'zh-CN'], id=None),
         'path': Value(dtype='string', id=None),
         'transcription': Value(dtype='string', id=None)}
        ```
        """
        info = self._info.copy()
        info.features[column] = feature
        # check that it's still valid, especially with regard to task templates
        try:
            info.copy()
        except ValueError:
            info.task_templates = None
        return iterable_dataset(
            ex_iterable=self._ex_iterable,
            info=info,
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def cast(
        self,
        features: Features,
    ) -> "IterableDataset":
        """
        Cast the dataset to a new set of features.

        Args:
            features (:class:`datasets.Features`): New features to cast the dataset to.
                The name of the fields in the features must match the current column names.
                The type of the data must also be convertible from one type to the other.
                For non-trivial conversion, e.g. string <-> ClassLabel you should use :func:`map` to update the Dataset.

        Returns:
            :class:`IterableDataset`: A copy of the dataset with casted features.

        Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="train", streaming=True)
        >>> ds.features
        {'label': ClassLabel(num_classes=2, names=['neg', 'pos'], id=None),
         'text': Value(dtype='string', id=None)}
        >>> new_features = ds.features.copy()
        >>> new_features["label"] = ClassLabel(names=["bad", "good"])
        >>> new_features["text"] = Value("large_string")
        >>> ds = ds.cast(new_features)
        >>> ds.features
        {'label': ClassLabel(num_classes=2, names=['bad', 'good'], id=None),
         'text': Value(dtype='large_string', id=None)}
        ```
        """
        info = self._info.copy()
        info.features = features
        # check that it's still valid, especially with regard to task templates
        try:
            info.copy()
        except ValueError:
            info.task_templates = None
        return iterable_dataset(
            ex_iterable=self._ex_iterable,
            info=info,
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )

    def _resolve_features(self):
        if self.features is not None:
            return self
        elif isinstance(self._ex_iterable, TypedExamplesIterable):
            features = self._ex_iterable.features
        else:
            features = _infer_features_from_batch(self._head())
        info = self.info.copy()
        info.features = features
        return iterable_dataset(
            ex_iterable=self._ex_iterable,
            info=info,
            split=self._split,
            format_type=self._format_type,
            shuffling=copy.deepcopy(self._shuffling),
            token_per_repo_id=self._token_per_repo_id,
        )


def iterable_dataset(
    ex_iterable: Iterable,
    info: Optional[DatasetInfo] = None,
    split: Optional[NamedSplit] = None,
    format_type: Optional[str] = None,
    shuffling: Optional[ShufflingConfig] = None,
    token_per_repo_id: Optional[Dict[str, Union[str, bool, None]]] = None,
):
    if format_type is not None and format_type == "torch":
        from .formatting.dataset_wrappers.torch_iterable_dataset import TorchIterableDataset

        cls = TorchIterableDataset
    else:
        cls = IterableDataset
    return cls(
        ex_iterable=ex_iterable,
        info=info,
        split=split,
        format_type=format_type,
        shuffling=shuffling,
        token_per_repo_id=token_per_repo_id,
    )


def _check_if_features_can_be_aligned(features_list: List[Features]):
    """Check if the dictionaries of features can be aligned.

    Two dictonaries of features can be aligned if the keys they share have the same type or some of them is of type `Value("null")`.
    """
    name2feature = {}
    for features in features_list:
        for k, v in features.items():
            if k not in name2feature or (isinstance(name2feature[k], Value) and name2feature[k].dtype == "null"):
                name2feature[k] = v

    for features in features_list:
        for k, v in features.items():
            if not (isinstance(v, Value) and v.dtype == "null") and name2feature[k] != v:
                raise ValueError(
                    f'The features can\'t be aligned because the key {k} of features {features} has unexpected type - {v} (expected either {name2feature[k]} or Value("null").'
                )


def _concatenate_iterable_datasets(
    dsets: List[IterableDataset],
    info: Optional[DatasetInfo] = None,
    split: Optional[NamedSplit] = None,
    axis: int = 0,
) -> IterableDataset:
    """
    Converts a list of :class:`IterableDataset` with the same schema into a single :class:`IterableDataset`.
    Missing data are filled with None values.

    Args:
        dsets (:obj:`List[datasets.IterableDataset]`): List of Datasets to concatenate.
        info (:class:`DatasetInfo`, optional): Dataset information, like description, citation, etc.
        split (:class:`NamedSplit`, optional): Name of the dataset split.
        axis (``{0, 1}``, default ``0``, meaning over rows):
            Axis to concatenate over, where ``0`` means over rows (vertically) and ``1`` means over columns
            (horizontally).

            *New in version 1.6.0*

    Example:

    ```py
    >>> ds3 = _concatenate_iterable_datasets([ds1, ds2])
    ```
    """
    dsets = [d._resolve_features() for d in dsets]

    # Perform checks (and a potentional cast if axis=0)
    if axis == 0:
        _check_if_features_can_be_aligned([dset.features for dset in dsets])
    else:
        _check_column_names([col_name for dset in dsets for col_name in dset.features])

    features = Features()
    for dset in dsets:
        features.update(dset.features)

    ex_iterables = [d._ex_iterable for d in dsets]
    if axis == 0:
        ex_iterable = VerticallyConcatenatedMultiSourcesExamplesIterable(ex_iterables)
    else:
        ex_iterable = HorizontallyConcatenatedMultiSourcesExamplesIterable(ex_iterables)
    # Set new info - we update the features
    # setting the features also ensures to fill missing columns with None
    if info is None:
        info = DatasetInfo.from_merge([d.info for d in dsets])
    else:
        info = info.copy()
    info.features = features
    # Get all the auth tokens per repository - in case the datasets come from different private repositories
    token_per_repo_id = {repo_id: token for dataset in dsets for repo_id, token in dataset._token_per_repo_id.items()}
    # Return new daset
    return iterable_dataset(ex_iterable=ex_iterable, info=info, split=split, token_per_repo_id=token_per_repo_id)


def _interleave_iterable_datasets(
    datasets: List[IterableDataset],
    probabilities: Optional[List[float]] = None,
    seed: Optional[int] = None,
    info: Optional[DatasetInfo] = None,
    split: Optional[NamedSplit] = None,
) -> IterableDataset:
    """
    Interleave several iterable datasets (sources) into a single iterable dataset.
    The new iterable dataset alternates between the sources to yield examples.
    If `probabilities = None` (default) the iterable dataset will cycles through the sources in order for each next example in the iteration.
    If `probabilities` is not `None, the iterable dataset will sample a random source according to the provided probabilities for each next examples in the iteration.

    Args:
        datasets (:obj:`List[IterableDataset]`): list of datasets to interleave
        probabilities (:obj:`List[float]`, optional, default None): If specified, the new iterable dataset samples
            examples from one source at a time according to these probabilities.
        seed (:obj:`int`, optional, default None): The random seed used to choose a source for each example.

    Output:
        :class:`datasets.IterableDataset`
    """
    # TODO(QL): merge the features as in _concatenate_iterable_datasets() and don't use TypedExamplesIterable
    ex_iterables = [
        TypedExamplesIterable(d._ex_iterable, d.features, token_per_repo_id=d._token_per_repo_id)
        if not isinstance(d._ex_iterable, TypedExamplesIterable) and d.features is not None
        else d._ex_iterable
        for d in datasets
    ]
    # Use cycling or random cycling or sources
    if probabilities is None:
        ex_iterable = CyclingMultiSourcesExamplesIterable(ex_iterables)
    else:
        generator = np.random.default_rng(seed)
        ex_iterable = RandomlyCyclingMultiSourcesExamplesIterable(
            ex_iterables, generator=generator, probabilities=probabilities
        )
    # Set new info - we reset the features
    # TODO(QL): merge the features as in _concatenate_iterable_datasets() and use them here
    if info is None:
        info = DatasetInfo.from_merge([d.info for d in datasets])
        info.features = None
    # Get all the auth tokens per repository - in case the datasets come from different private repositories
    token_per_repo_id = {
        repo_id: token for dataset in datasets for repo_id, token in dataset._token_per_repo_id.items()
    }
    # Return new daset
    return iterable_dataset(ex_iterable=ex_iterable, info=info, split=split, token_per_repo_id=token_per_repo_id)