token_indexer.py

from typing import Any, Dict, List

import torch

from allennlp.common import Registrable
from allennlp.common.util import pad_sequence_to_length
from allennlp.data.tokenizers import Token
from allennlp.data.vocabulary import Vocabulary

# An indexed token list represents the arguments that will be passed to a TokenEmbedder
# corresponding to this TokenIndexer.  Each argument that the TokenEmbedder needs will have one
# entry in the IndexedTokenList dictionary, and that argument will typically be a list of integers
# (for single ID word embeddings) or a nested list of integers (for character ID word embeddings),
# though it could also be a mask, or any other data that you want to pass.
IndexedTokenList = Dict[str, List[Any]]


class TokenIndexer(Registrable):
    """
    A `TokenIndexer` determines how string tokens get represented as arrays of indices in a model.
    This class both converts strings into numerical values, with the help of a
    :class:`~allennlp.data.vocabulary.Vocabulary`, and it produces actual arrays.

    Tokens can be represented as single IDs (e.g., the word "cat" gets represented by the number
    34), or as lists of character IDs (e.g., "cat" gets represented by the numbers [23, 10, 18]),
    or in some other way that you can come up with (e.g., if you have some structured input you
    want to represent in a special way in your data arrays, you can do that here).

    # Parameters

    token_min_padding_length : `int`, optional (default=`0`)
        The minimum padding length required for the :class:`TokenIndexer`. For example,
        the minimum padding length of :class:`SingleIdTokenIndexer` is the largest size of
        filter when using :class:`CnnEncoder`.
        Note that if you set this for one TokenIndexer, you likely have to set it for all
        :class:`TokenIndexer` for the same field, otherwise you'll get mismatched tensor sizes.
    """

    default_implementation = "single_id"
    has_warned_for_as_padded_tensor = False

    def __init__(self, token_min_padding_length: int = 0) -> None:
        self._token_min_padding_length: int = token_min_padding_length

    def count_vocab_items(self, token: Token, counter: Dict[str, Dict[str, int]]):
        """
        The :class:`Vocabulary` needs to assign indices to whatever strings we see in the training
        data (possibly doing some frequency filtering and using an OOV, or out of vocabulary,
        token).  This method takes a token and a dictionary of counts and increments counts for
        whatever vocabulary items are present in the token.  If this is a single token ID
        representation, the vocabulary item is likely the token itself.  If this is a token
        characters representation, the vocabulary items are all of the characters in the token.
        """
        raise NotImplementedError

    def tokens_to_indices(self, tokens: List[Token], vocabulary: Vocabulary) -> IndexedTokenList:
        """
        Takes a list of tokens and converts them to an `IndexedTokenList`.
        This could be just an ID for each token from the vocabulary.
        Or it could split each token into characters and return one ID per character.
        Or (for instance, in the case of byte-pair encoding) there might not be a clean
        mapping from individual tokens to indices, and the `IndexedTokenList` could be a complex
        data structure.
        """
        raise NotImplementedError

    def indices_to_tokens(
        self, indexed_tokens: IndexedTokenList, vocabulary: Vocabulary
    ) -> List[Token]:
        """
        Inverse operations of tokens_to_indices. Takes an `IndexedTokenList` and converts it back
        into a list of tokens.
        """
        raise NotImplementedError

    def get_empty_token_list(self) -> IndexedTokenList:
        """
        Returns an `already indexed` version of an empty token list.  This is typically just an
        empty list for whatever keys are used in the indexer.
        """
        raise NotImplementedError

    def get_padding_lengths(self, indexed_tokens: IndexedTokenList) -> Dict[str, int]:
        """
        This method returns a padding dictionary for the given `indexed_tokens` specifying all
        lengths that need padding.  If all you have is a list of single ID tokens, this is just the
        length of the list, and that's what the default implementation will give you.  If you have
        something more complicated, like a list of character ids for token, you'll need to override
        this.
        """
        padding_lengths = {}
        for key, token_list in indexed_tokens.items():
            padding_lengths[key] = max(len(token_list), self._token_min_padding_length)
        return padding_lengths

    def as_padded_tensor_dict(
        self, tokens: IndexedTokenList, padding_lengths: Dict[str, int]
    ) -> Dict[str, torch.Tensor]:
        """
        This method pads a list of tokens given the input padding lengths (which could actually
        truncate things, depending on settings) and returns that padded list of input tokens as a
        `Dict[str, torch.Tensor]`.  This is a dictionary because there should be one key per
        argument that the `TokenEmbedder` corresponding to this class expects in its `forward()`
        method (where the argument name in the `TokenEmbedder` needs to make the key in this
        dictionary).

        The base class implements the case when all you want to do is create a padded `LongTensor`
        for every list in the `tokens` dictionary.  If your `TokenIndexer` needs more complex
        logic than that, you need to override this method.
        """
        tensor_dict = {}
        for key, val in tokens.items():
            if val and isinstance(val[0], bool):
                tensor = torch.BoolTensor(
                    pad_sequence_to_length(val, padding_lengths[key], default_value=lambda: False)
                )
            else:
                tensor = torch.LongTensor(pad_sequence_to_length(val, padding_lengths[key]))
            tensor_dict[key] = tensor
        return tensor_dict

    def __eq__(self, other) -> bool:
        if isinstance(self, other.__class__):
            return self.__dict__ == other.__dict__
        return NotImplemented