embedding_ops.py

# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Operations for embeddings."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from six.moves import xrange  # pylint: disable=redefined-builtin

from tensorflow.python.compat import compat
from tensorflow.python.framework import constant_op
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import ops
from tensorflow.python.framework import sparse_tensor
from tensorflow.python.framework import tensor_shape
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import clip_ops
# Imports gradient definitions.
from tensorflow.python.ops import data_flow_grad  # pylint: disable=unused-import
from tensorflow.python.ops import data_flow_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import resource_variable_ops
from tensorflow.python.ops import sparse_ops
from tensorflow.python.ops import variables
from tensorflow.python.ops.ragged import ragged_functional_ops
from tensorflow.python.ops.ragged import ragged_tensor
from tensorflow.python.util import dispatch
from tensorflow.python.util.tf_export import tf_export


def _clip(params, ids, max_norm):
  """Helper function for _embedding_lookup_and_transform.

  This function optionally clips embeddings to an l2-norm of max_norm.

  Args:
    params: A `Tensor` of embeddings retrieved by `gather`.
    ids: The `ids` argument that was passed to `gather`.
    max_norm: If not `None`, each embedding is clipped if its l2-norm is larger
      than this value.

  Returns:
    A `Tensor` with the same type as `params`.
  """

  def _rank(x):
    """Helper function to retrieve the rank of a tensor.

    Args:
      x: Something convertible to `Tensor`.

    Returns:
      Either a pair `(rank, True)` where `rank` is an integer or a pair
      `(rank, False)` where `rank` is an integer `Tensor`. In either case,
      `rank` is the rank of `x`.
    """
    rank = ops.convert_to_tensor(x).get_shape().ndims
    if rank:
      return rank, True
    else:
      return array_ops.rank(x), False

  if max_norm is None:
    return params
  ids_rank, ids_static = _rank(ids)
  params_rank, params_static = _rank(params)
  return clip_ops.clip_by_norm(
      params,
      max_norm,
      axes=(list(range(ids_rank, params_rank)) if ids_static and params_static
            else math_ops.range(ids_rank, params_rank)))


def _embedding_lookup_and_transform(params,
                                    ids,
                                    partition_strategy="mod",
                                    name=None,
                                    max_norm=None,
                                    transform_fn=None):
  """Helper function for embedding_lookup and _compute_sampled_logits.

  This function is a generalization of embedding_lookup that optionally
  applies a caller-specified transformation to each embedding. This is
  done through the `transform_fn` argument. If provided, the function is
  applied to each partitioned tensor of retrieved embeddings, colocated
  with the embeddings. This function will be called with a single `Tensor`
  argument of the same type as the `params` tensor and should return a
  `Tensor`. The shape of the argument will be the same as `params` except
  for the size of the first dimension. The first dimension of the result's
  shape must be the same size as the argument's.

  Args:
    params: See embedding_lookup.
    ids: See embedding_lookup.
    partition_strategy: See embedding_lookup.
    name: See embedding_lookup.
    max_norm: See embedding_lookup.
    transform_fn: An optional function to apply to each retrieved embedding. If
      max_norm is provided, transform_fn is applied to the norm-limited
      embeddings.

  Returns:
    See embedding_lookup for details.
  Raises:
    ValueError: If `params` is empty.
  """
  if params is None:
    raise ValueError("params must be specified")
  if isinstance(params, (list, tuple)) and not params:
    raise ValueError("Need at least one param")
  if isinstance(params, variables.PartitionedVariable):
    params = list(params)  # Iterate to get the underlying Variables.
  if not isinstance(params, list):
    params = [params]

  with ops.name_scope(name, "embedding_lookup", params + [ids]) as name:
    np = len(params)  # Number of partitions
    # Preserve the resource variable status to avoid accidental dense reads.
    if not any(
        isinstance(p, resource_variable_ops.ResourceVariable) for p in params):
      params = ops.convert_n_to_tensor_or_indexed_slices(params, name="params")
    ids = ops.convert_to_tensor(ids, name="ids")
    if np == 1 and (not transform_fn or ids.get_shape().ndims == 1):
      with ops.colocate_with(params[0]):
        result = _clip(
            array_ops.gather(params[0], ids, name=name), ids, max_norm)
        if transform_fn:
          result = transform_fn(result)
      # Make sure the final result does not have colocation constraints on the
      # params. Similar to the case np > 1 where parallel_dynamic_stitch is
      # outside the scioe of all with ops.colocate_with(params[p]).
      return array_ops.identity(result)
    else:
      # Flatten the ids. There are two cases where we need to do this.
      # - There is more than one params tensor.
      # - There is a transform_fn and ids is not statically known to be 1-D.
      #   We must flatten in this case because transform_fn expects a flat
      #   tensor of embeddings.
      flat_ids = array_ops.reshape(ids, [-1])
      original_indices = math_ops.range(array_ops.size(flat_ids))

      # Create p_assignments and set new_ids depending on the strategy.
      if partition_strategy == "mod":
        p_assignments = flat_ids % np
        new_ids = flat_ids // np
      elif partition_strategy == "div":
        # Compute num_total_ids as the sum of dim-0 of params, then assign to
        # partitions based on a constant number of ids per partition. Optimize
        # if we already know the full shape statically.
        dim_0_size = tensor_shape.Dimension(
            tensor_shape.dimension_value(params[0].get_shape()[0]))
        for p in xrange(1, np):
          dim_0_size += tensor_shape.Dimension(
              tensor_shape.dimension_value(params[p].get_shape()[0]))
        if dim_0_size.value:
          num_total_ids = constant_op.constant(dim_0_size.value, flat_ids.dtype)
        else:
          dim_0_sizes = []
          for p in xrange(np):
            param_p_dim = tensor_shape.dimension_value(params[p].get_shape()[0])
            if param_p_dim is not None:
              dim_0_sizes.append(param_p_dim)
            else:
              with ops.colocate_with(params[p]):
                dim_0_sizes.append(array_ops.shape(params[p])[0])
          num_total_ids = math_ops.reduce_sum(
              math_ops.cast(array_ops.stack(dim_0_sizes), flat_ids.dtype))
        ids_per_partition = num_total_ids // np
        extras = num_total_ids % np

        p_assignments = math_ops.maximum(flat_ids // (ids_per_partition + 1),
                                         (flat_ids - extras) //
                                         ids_per_partition)

        # Emulate a conditional using a boolean indicator tensor
        new_ids = array_ops.where(p_assignments < extras,
                                  flat_ids % (ids_per_partition + 1),
                                  (flat_ids - extras) % ids_per_partition)
      else:
        raise ValueError("Unrecognized partition strategy: " +
                         partition_strategy)

      # Cast partition assignments to int32 for use in dynamic_partition.
      # There really should not be more than 2^32 partitions.
      p_assignments = math_ops.cast(p_assignments, dtypes.int32)
      # Partition list of ids based on assignments into np separate lists
      gather_ids = data_flow_ops.dynamic_partition(new_ids, p_assignments, np)
      # Similarly, partition the original indices.
      pindices = data_flow_ops.dynamic_partition(original_indices,
                                                 p_assignments, np)
      # Do np separate lookups, finding embeddings for plist[p] in params[p]
      partitioned_result = []
      for p in xrange(np):
        pids = gather_ids[p]
        with ops.colocate_with(params[p]):
          result = array_ops.gather(params[p], pids)
          if transform_fn:
            # If transform_fn is provided, the clip_by_norm precedes
            # the transform and hence must be co-located. See below
            # for the counterpart if transform_fn is not provided.
            result = transform_fn(_clip(result, pids, max_norm))
        partitioned_result.append(result)
      # Stitch these back together
      ret = data_flow_ops.parallel_dynamic_stitch(
          pindices, partitioned_result, name=name)

      # Determine the static element shape.
      if transform_fn is None:
        element_shape_s = params[0].get_shape()[1:]
        for p in params[1:]:
          element_shape_s = element_shape_s.merge_with(p.get_shape()[1:])
      else:
        element_shape_s = ret.get_shape()[1:]

      # Compute the dynamic element shape.
      if element_shape_s.is_fully_defined():
        element_shape_d = element_shape_s
      elif transform_fn is None:
        # It's important that we compute params[0].shape on the right device
        # to avoid data motion.
        with ops.colocate_with(params[0]):
          params_shape = array_ops.shape(params[0])
        element_shape_d = params_shape[1:]
      else:
        element_shape_d = array_ops.shape(ret)[1:]

      # Reshape to reverse the flattening of ids.
      ret = array_ops.reshape(
          ret, array_ops.concat([array_ops.shape(ids), element_shape_d], 0))

      # Normally the reshape is sufficient, but setting shape explicitly
      # teaches shape inference that params[1:].get_shape() matters
      # (in the case that transform_fn is None).
      ret.set_shape(ids.get_shape().concatenate(element_shape_s))
      if not transform_fn:
        # If transform_fn was provided, the clip_by_norm was done above.
        ret = _clip(ret, ids, max_norm)
      return ret


@tf_export(v1=["nn.embedding_lookup"])
@dispatch.add_dispatch_support
def embedding_lookup(
    params,
    ids,
    partition_strategy="mod",
    name=None,
    validate_indices=True,  # pylint: disable=unused-argument
    max_norm=None):
  """Looks up embeddings for the given `ids` from a list of tensors.

  This function is used to perform parallel lookups on the list of tensors in
  `params`.  It is a generalization of `tf.gather`, where `params` is
  interpreted as a partitioning of a large embedding tensor.  `params` may be
  a `PartitionedVariable` as returned by using `tf.compat.v1.get_variable()`
  with a partitioner.

  If `len(params) > 1`, each element `id` of `ids` is partitioned between
  the elements of `params` according to the `partition_strategy`.
  In all strategies, if the id space does not evenly divide the number of
  partitions, each of the first `(max_id + 1) % len(params)` partitions will
  be assigned one more id.

  If `partition_strategy` is `"mod"`, we assign each id to partition
  `p = id % len(params)`. For instance,
  13 ids are split across 5 partitions as:
  `[[0, 5, 10], [1, 6, 11], [2, 7, 12], [3, 8], [4, 9]]`

  If `partition_strategy` is `"div"`, we assign ids to partitions in a
  contiguous manner. In this case, 13 ids are split across 5 partitions as:
  `[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10], [11, 12]]`

  If the input ids are ragged tensors, partition variables are not supported and
  the partition strategy and the max_norm are ignored.
  The results of the lookup are concatenated into a dense
  tensor. The returned tensor has shape `shape(ids) + shape(params)[1:]`.

  Args:
    params: A single tensor representing the complete embedding tensor, or a
      list of P tensors all of same shape except for the first dimension,
      representing sharded embedding tensors.  Alternatively, a
      `PartitionedVariable`, created by partitioning along dimension 0. Each
      element must be appropriately sized for the given `partition_strategy`.
    ids: A `Tensor` or a 'RaggedTensor' with type `int32` or `int64` containing
      the ids to be looked up in `params`.
    partition_strategy: A string specifying the partitioning strategy, relevant
      if `len(params) > 1`. Currently `"div"` and `"mod"` are supported. Default
      is `"mod"`.
    name: A name for the operation (optional).
    validate_indices: DEPRECATED. If this operation is assigned to CPU, values
      in `indices` are always validated to be within range.  If assigned to GPU,
      out-of-bound indices result in safe but unspecified behavior, which may
      include raising an error.
    max_norm: If not `None`, each embedding is clipped if its l2-norm is larger
      than this value.

  Returns:
    A `Tensor` or a 'RaggedTensor', depending on the input, with the same type
    as the tensors in `params`.

  Raises:
    ValueError: If `params` is empty.
  """
  if isinstance(ids, ragged_tensor.RaggedTensor):
    return embedding_lookup_ragged(params, ids,
                                   partition_strategy=partition_strategy,
                                   max_norm=max_norm,
                                   name=name)

  return _embedding_lookup_and_transform(
      params=params,
      ids=ids,
      partition_strategy=partition_strategy,
      name=name,
      max_norm=max_norm,
      transform_fn=None)


@tf_export("nn.embedding_lookup", v1=[])
@dispatch.add_dispatch_support
def embedding_lookup_v2(params, ids, max_norm=None, name=None):
  """Looks up embeddings for the given `ids` from a list of tensors.

  This function is used to perform parallel lookups on the list of tensors in
  `params`.  It is a generalization of `tf.gather`, where `params` is
  interpreted as a partitioning of a large embedding tensor.

  If `len(params) > 1`, each element `id` of `ids` is partitioned between the
  elements of `params` according to the "div" partition strategy, which means we
  assign ids to partitions in a contiguous manner. For instance, 13 ids are
  split across 5 partitions as:
  `[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10], [11, 12]]`.

  If the id space does not evenly divide the number of partitions, each of the
  first `(max_id + 1) % len(params)` partitions will be assigned one more id.

  The results of the lookup are concatenated into a dense
  tensor. The returned tensor has shape `shape(ids) + shape(params)[1:]`.

  Args:
    params: A single tensor representing the complete embedding tensor, or a
      list of tensors all of same shape except for the first dimension,
      representing sharded embedding tensors following "div" partition strategy.
    ids: A `Tensor` with type `int32` or `int64` containing the ids to be looked
      up in `params`.
    max_norm: If not `None`, each embedding is clipped if its l2-norm is larger
      than this value.
    name: A name for the operation (optional).

  Returns:
    A `Tensor` with the same type as the tensors in `params`.

    For instance, if `params` is a 5x2 matrix:

    ```python
    [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]
    ```

    or a list of matrices:

    ```python
    params[0]: [[1, 2], [3, 4]]
    params[1]: [[5, 6], [7, 8]]
    params[2]: [[9, 10]]
    ```

    and `ids` is:

    ```python
    [0, 3, 4]
    ```

    The output will be a 3x2 matrix:

    ```python
    [[1, 2], [7, 8], [9, 10]]
    ```

  Raises:
    ValueError: If `params` is empty.
  """
  return embedding_lookup(params, ids, "div", name, max_norm=max_norm)


@tf_export(v1=["nn.embedding_lookup_sparse"])
@dispatch.add_dispatch_support
def embedding_lookup_sparse(params,
                            sp_ids,
                            sp_weights,
                            partition_strategy="mod",
                            name=None,
                            combiner=None,
                            max_norm=None):
  """Looks up embeddings for the given ids and weights from a list of tensors.

  This op assumes that there is at least one id for each row in the dense tensor
  represented by sp_ids (i.e. there are no rows with empty features), and that
  all the indices of sp_ids are in canonical row-major order.

  `sp_ids` and `sp_weights` (if not None) are `SparseTensor`s with rank of 2.
  Embeddings are always aggregated along the last dimension.

  It also assumes that all id values lie in the range [0, p0), where p0
  is the sum of the size of params along dimension 0.

  Args:
    params: A single tensor representing the complete embedding tensor, or a
      list tensors all of same shape except for the first dimension,
      representing sharded embedding tensors. Alternatively, a
      `PartitionedVariable`, created by partitioning along dimension 0. Each
      element must be appropriately sized for the given `partition_strategy`.
    sp_ids: N x M `SparseTensor` of int64 ids where N is typically batch size
      and M is arbitrary.
    sp_weights: either a `SparseTensor` of float / double weights, or `None` to
      indicate all weights should be taken to be 1. If specified, `sp_weights`
      must have exactly the same shape and indices as `sp_ids`.
    partition_strategy: A string specifying the partitioning strategy, relevant
      if `len(params) > 1`. Currently `"div"` and `"mod"` are supported. Default
      is `"mod"`. See `tf.nn.embedding_lookup` for more details.
    name: Optional name for the op.
    combiner: A string specifying the reduction op. Currently "mean", "sqrtn"
      and "sum" are supported. "sum" computes the weighted sum of the embedding
      results for each row. "mean" is the weighted sum divided by the total
      weight. "sqrtn" is the weighted sum divided by the square root of the sum
      of the squares of the weights. Defaults to `mean`.
    max_norm: If not `None`, each embedding is clipped if its l2-norm is larger
      than this value, before combining.

  Returns:
    A dense tensor representing the combined embeddings for the
    sparse ids. For each row in the dense tensor represented by `sp_ids`, the op
    looks up the embeddings for all ids in that row, multiplies them by the
    corresponding weight, and combines these embeddings as specified.

    In other words, if

      `shape(combined params) = [p0, p1, ..., pm]`

    and

      `shape(sp_ids) = shape(sp_weights) = [d0, d1]`

    then

      `shape(output) = [d0, p1, ..., pm]`.

    For instance, if params is a 10x20 matrix, and sp_ids / sp_weights are

      ```python
      [0, 0]: id 1, weight 2.0
      [0, 1]: id 3, weight 0.5
      [1, 0]: id 0, weight 1.0
      [2, 3]: id 1, weight 3.0
      ```

    with `combiner`="mean", then the output will be a 3x20 matrix where

      ```python
      output[0, :] = (params[1, :] * 2.0 + params[3, :] * 0.5) / (2.0 + 0.5)
      output[1, :] = (params[0, :] * 1.0) / 1.0
      output[2, :] = (params[1, :] * 3.0) / 3.0
      ```

  Raises:
    TypeError: If `sp_ids` is not a `SparseTensor`, or if `sp_weights` is
      neither `None` nor `SparseTensor`.
    ValueError: If `combiner` is not one of {"mean", "sqrtn", "sum"}.
  """
  if combiner is None:
    combiner = "mean"
  if combiner not in ("mean", "sqrtn", "sum"):
    raise ValueError("combiner must be one of 'mean', 'sqrtn' or 'sum'")
  if isinstance(params, variables.PartitionedVariable):
    params = list(params)  # Iterate to get the underlying Variables.
  if not isinstance(params, list):
    params = [params]
  if not isinstance(sp_ids, sparse_tensor.SparseTensor):
    raise TypeError("sp_ids must be SparseTensor")
  ignore_weights = sp_weights is None
  if not ignore_weights:
    if not isinstance(sp_weights, sparse_tensor.SparseTensor):
      raise TypeError("sp_weights must be either None or SparseTensor")
    sp_ids.values.get_shape().assert_is_compatible_with(
        sp_weights.values.get_shape())
    sp_ids.indices.get_shape().assert_is_compatible_with(
        sp_weights.indices.get_shape())
    sp_ids.dense_shape.get_shape().assert_is_compatible_with(
        sp_weights.dense_shape.get_shape())
    # TODO(yleon): Add enhanced node assertions to verify that sp_ids and
    # sp_weights have equal indices and shapes.

  with ops.name_scope(name, "embedding_lookup_sparse",
                      params + [sp_ids]) as name:
    segment_ids = sp_ids.indices[:, 0]

    ids = sp_ids.values
    ids, idx = array_ops.unique(ids)

    embeddings = embedding_lookup(
        params, ids, partition_strategy=partition_strategy, max_norm=max_norm)
    if embeddings.dtype in (dtypes.float16, dtypes.bfloat16):
      embeddings = math_ops.cast(embeddings, dtypes.float32)
    if not ignore_weights:
      if segment_ids.dtype != dtypes.int32:
        segment_ids = math_ops.cast(segment_ids, dtypes.int32)

      weights = sp_weights.values
      if weights.dtype != embeddings.dtype:
        weights = math_ops.cast(weights, embeddings.dtype)

      embeddings = array_ops.gather(embeddings, idx)

      # Reshape weights to allow broadcast
      ones = array_ops.fill(
          array_ops.expand_dims(array_ops.rank(embeddings) - 1, 0), 1)
      bcast_weights_shape = array_ops.concat([array_ops.shape(weights), ones],
                                             0)

      orig_weights_shape = weights.get_shape()
      weights = array_ops.reshape(weights, bcast_weights_shape)

      # Set the weight shape, since after reshaping to bcast_weights_shape,
      # the shape becomes None.
      if embeddings.get_shape().ndims is not None:
        weights.set_shape(
            orig_weights_shape.concatenate(
                [1 for _ in range(embeddings.get_shape().ndims - 1)]))

      embeddings *= weights

      if combiner == "sum":
        embeddings = math_ops.segment_sum(embeddings, segment_ids, name=name)
      elif combiner == "mean":
        embeddings = math_ops.segment_sum(embeddings, segment_ids)
        weight_sum = math_ops.segment_sum(weights, segment_ids)
        embeddings = math_ops.divide(embeddings, weight_sum, name=name)
      elif combiner == "sqrtn":
        embeddings = math_ops.segment_sum(embeddings, segment_ids)
        weights_squared = math_ops.pow(weights, 2)
        weight_sum = math_ops.segment_sum(weights_squared, segment_ids)
        weight_sum_sqrt = math_ops.sqrt(weight_sum)
        embeddings = math_ops.divide(embeddings, weight_sum_sqrt, name=name)
      else:
        assert False, "Unrecognized combiner"
    else:
      if compat.forward_compatible(2020, 5, 14):
        if segment_ids.dtype not in (dtypes.int32, dtypes.int64):
          segment_ids = math_ops.cast(segment_ids, dtypes.int32)
      else:
        if segment_ids.dtype != dtypes.int32:
          segment_ids = math_ops.cast(segment_ids, dtypes.int32)
      assert idx is not None
      if combiner == "sum":
        embeddings = math_ops.sparse_segment_sum(
            embeddings, idx, segment_ids, name=name)
      elif combiner == "mean":
        embeddings = math_ops.sparse_segment_mean(
            embeddings, idx, segment_ids, name=name)
      elif combiner == "sqrtn":
        embeddings = math_ops.sparse_segment_sqrt_n(
            embeddings, idx, segment_ids, name=name)
      else:
        assert False, "Unrecognized combiner"

    return embeddings


@tf_export("nn.embedding_lookup_sparse", v1=[])
@dispatch.add_dispatch_support
def embedding_lookup_sparse_v2(params,
                               sp_ids,
                               sp_weights,
                               combiner=None,
                               max_norm=None,
                               name=None):
  """Looks up embeddings for the given ids and weights from a list of tensors.

  This op assumes that there is at least one id for each row in the dense tensor
  represented by sp_ids (i.e. there are no rows with empty features), and that
  all the indices of sp_ids are in canonical row-major order.

  `sp_ids` and `sp_weights` (if not None) are `SparseTensor`s with rank of 2.
  Embeddings are always aggregated along the last dimension.

  It also assumes that all id values lie in the range [0, p0), where p0
  is the sum of the size of params along dimension 0.

  If `len(params) > 1`, each element of `sp_ids` is partitioned between the
  elements of `params` according to the "div" partition strategy, which means we
  assign ids to partitions in a contiguous manner. For instance, 13 ids are
  split across 5 partitions as:
  `[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10], [11, 12]]`.

  If the id space does not evenly divide the number of partitions, each of the
  first `(max_id + 1) % len(params)` partitions will be assigned one more id.

  Args:
    params: A single tensor representing the complete embedding tensor, or a
      list of tensors all of same shape except for the first dimension,
      representing sharded embedding tensors following "div" partition strategy.
    sp_ids: N x M `SparseTensor` of int64 ids where N is typically batch size
      and M is arbitrary.
    sp_weights: either a `SparseTensor` of float / double weights, or `None` to
      indicate all weights should be taken to be 1. If specified, `sp_weights`
      must have exactly the same shape and indices as `sp_ids`.
    combiner: A string specifying the reduction op. Currently "mean", "sqrtn"
      and "sum" are supported. "sum" computes the weighted sum of the embedding
      results for each row. "mean" is the weighted sum divided by the total
      weight. "sqrtn" is the weighted sum divided by the square root of the sum
      of the squares of the weights. Defaults to `mean`.
    max_norm: If not `None`, each embedding is clipped if its l2-norm is larger
      than this value, before combining.
    name: Optional name for the op.

  Returns:
    A dense tensor representing the combined embeddings for the
    sparse ids. For each row in the dense tensor represented by `sp_ids`, the op
    looks up the embeddings for all ids in that row, multiplies them by the
    corresponding weight, and combines these embeddings as specified.

    In other words, if

      `shape(combined params) = [p0, p1, ..., pm]`

    and

      `shape(sp_ids) = shape(sp_weights) = [d0, d1]`

    then

      `shape(output) = [d0, p1, ..., pm]`.

    For instance, if params is a 10x20 matrix, and sp_ids / sp_weights are

      ```python
      [0, 0]: id 1, weight 2.0
      [0, 1]: id 3, weight 0.5
      [1, 0]: id 0, weight 1.0
      [2, 3]: id 1, weight 3.0
      ```

    with `combiner`="mean", then the output will be a 3x20 matrix where

      ```python
      output[0, :] = (params[1, :] * 2.0 + params[3, :] * 0.5) / (2.0 + 0.5)
      output[1, :] = (params[0, :] * 1.0) / 1.0
      output[2, :] = (params[1, :] * 3.0) / 3.0
      ```

  Raises:
    TypeError: If `sp_ids` is not a `SparseTensor`, or if `sp_weights` is
      neither `None` nor `SparseTensor`.
    ValueError: If `combiner` is not one of {"mean", "sqrtn", "sum"}.
  """
  return embedding_lookup_sparse(params, sp_ids, sp_weights, "div", name,
                                 combiner, max_norm)


@tf_export("nn.safe_embedding_lookup_sparse", v1=[])
@dispatch.add_dispatch_support
def safe_embedding_lookup_sparse_v2(embedding_weights,
                                    sparse_ids,
                                    sparse_weights=None,
                                    combiner="mean",
                                    default_id=None,
                                    max_norm=None,
                                    name=None):
  """Lookup embedding results, accounting for invalid IDs and empty features.

  The partitioned embedding in `embedding_weights` must all be the same shape
  except for the first dimension. The first dimension is allowed to vary as the
  vocabulary size is not necessarily a multiple of num of shards.

  Invalid IDs (< 0) are pruned from input IDs and weights, as well as any IDs
  with non-positive weight. For an entry with no features, the embedding vector
  for `default_id` is returned, or the 0-vector if `default_id` is not supplied.

  The ids and weights may be multi-dimensional. Embeddings are always aggregated
  along the last dimension.

  If `len(embedding_weights) > 1`, each element `id` of `ids` is partitioned
  between the elements of `embedding_weights` according to the "div" partition
  strategy, which means we assign ids to partitions in a contiguous manner. For
  instance, 13 ids are split across 5 partitions as:
  `[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10], [11, 12]]`.

  If the id space does not evenly divide the number of partitions, each of the
  first `(max_id + 1) % len(embedding_weights)` partitions will be assigned one
  more id.

  Args:
    embedding_weights: A single tensor representing the complete embedding
      tensor, or a list of tensors all of same shape except for the first
      dimension, representing sharded embedding tensors following "div"
      partition strategy.
    sparse_ids: `SparseTensor` of shape `[d_0, d_1, ..., d_n]` containing the
      ids. `d_0` is typically batch size.
    sparse_weights: `SparseTensor` of same shape as `sparse_ids`, containing
      float weights corresponding to `sparse_ids`, or `None` if all weights are
      be assumed to be 1.0.
    combiner: A string specifying how to combine embedding results for each
      entry. Currently "mean", "sqrtn" and "sum" are supported, with "mean" the
      default.
    default_id: The id to use for an entry with no features. Defaults to
      0-vector.
    max_norm: If not `None`, all embeddings are l2-normalized to max_norm before
      combining.
    name: A name for this operation (optional).

  Returns:
    A dense tensor representing the combined embeddings for the
    sparse ids. For each row in the dense tensor represented by `sparse_ids`,
    the op looks up the embeddings for all ids in that row, multiplies them by
    the corresponding weight, and combines these embeddings as specified.

    In other words, if

      `shape(combined embedding_weights) = [p0, p1, ..., pm]`

    and

      `shape(sparse_ids) = shape(sparse_weights) = [d0, d1, ..., dn]`

    then

      `shape(output) = [d0, d1, ... dn-1, p1, ..., pm]`.

    For instance, if params is a 10x20 matrix, and sp_ids / sp_weights are

      ```python
      [0, 0]: id 1, weight 2.0
      [0, 1]: id 3, weight 0.5
      [1, 0]: id -1, weight 1.0
      [2, 3]: id 1, weight 3.0
      ```

    `default_id` is 0.

    with `combiner`="mean", then the output will be a 3x20 matrix where

      ```python
      output[0, :] = (params[1, :] * 2.0 + params[3, :] * 0.5) / (2.0 + 0.5)
      output[1, :] = (params[0, :] * 1.0) / 1.0
      output[2, :] = (params[1, :] * 3.0) / 3.0
      ```

  Raises:
    ValueError: if `embedding_weights` is empty.
  """
  return safe_embedding_lookup_sparse(
      embedding_weights,
      sparse_ids,
      sparse_weights=sparse_weights,
      combiner=combiner,
      default_id=default_id,
      name=name,
      partition_strategy="div",
      max_norm=max_norm)


@tf_export(v1=["nn.safe_embedding_lookup_sparse"])
@dispatch.add_dispatch_support
def safe_embedding_lookup_sparse(embedding_weights,
                                 sparse_ids,
                                 sparse_weights=None,
                                 combiner="mean",
                                 default_id=None,
                                 name=None,
                                 partition_strategy="div",
                                 max_norm=None):
  """Lookup embedding results, accounting for invalid IDs and empty features.

  The partitioned embedding in `embedding_weights` must all be the same shape
  except for the first dimension. The first dimension is allowed to vary as the
  vocabulary size is not necessarily a multiple of `P`.  `embedding_weights`
  may be a `PartitionedVariable` as returned by using
  `tf.compat.v1.get_variable()` with a
  partitioner.

  Invalid IDs (< 0) are pruned from input IDs and weights, as well as any IDs
  with non-positive weight. For an entry with no features, the embedding vector
  for `default_id` is returned, or the 0-vector if `default_id` is not supplied.

  The ids and weights may be multi-dimensional. Embeddings are always aggregated
  along the last dimension.

  Args:
    embedding_weights: A single tensor representing the complete embedding
      tensor, or a list tensors all of same shape except for the first
      dimension, representing sharded embedding tensors. Alternatively, a
      `PartitionedVariable`, created by partitioning along dimension 0. Each
      element must be appropriately sized for the given `partition_strategy`.
    sparse_ids: `SparseTensor` of shape `[d_0, d_1, ..., d_n]` containing the
      ids. `d_0` is typically batch size.
    sparse_weights: `SparseTensor` of same shape as `sparse_ids`, containing
      float weights corresponding to `sparse_ids`, or `None` if all weights are
      be assumed to be 1.0.
    combiner: A string specifying how to combine embedding results for each
      entry. Currently "mean", "sqrtn" and "sum" are supported, with "mean" the
      default.
    default_id: The id to use for an entry with no features.
    name: A name for this operation (optional).
    partition_strategy: A string specifying the partitioning strategy. Currently
      `"div"` and `"mod"` are supported. Default is `"div"`.
    max_norm: If not `None`, all embeddings are l2-normalized to max_norm before
      combining.

  Returns:
    A dense tensor representing the combined embeddings for the
    sparse ids. For each row in the dense tensor represented by `sp_ids`, the op
    looks up the embeddings for all ids in that row, multiplies them by the
    corresponding weight, and combines these embeddings as specified.

    In other words, if

      `shape(combined embedding_weights) = [p0, p1, ..., pm]`

    and

      `shape(sparse_ids) = shape(sparse_weights) = [d0, d1, ..., dn]`

    then

      `shape(output) = [d0, d1, ... dn-1, p1, ..., pm]`.

    For instance, if params is a 10x20 matrix, and sp_ids / sp_weights are

      ```python
      [0, 0]: id 1, weight 2.0
      [0, 1]: id 3, weight 0.5
      [1, 0]: id -1, weight 1.0
      [2, 3]: id 1, weight 3.0
      ```

    `default_id` is 0.

    with `combiner`="mean", then the output will be a 3x20 matrix where

      ```python
      output[0, :] = (params[1, :] * 2.0 + params[3, :] * 0.5) / (2.0 + 0.5)
      output[1, :] = (params[0, :] * 1.0) / 1.0
      output[2, :] = (params[1, :] * 3.0) / 3.0
      ```

  Raises:
    ValueError: if `embedding_weights` is empty.
  """
  if embedding_weights is None:
    raise ValueError("Missing embedding_weights %s." % embedding_weights)
  if isinstance(embedding_weights, variables.PartitionedVariable):
    embedding_weights = list(embedding_weights)  # get underlying Variables.
  if not isinstance(embedding_weights, list):
    embedding_weights = [embedding_weights]
  if len(embedding_weights) < 1:
    raise ValueError("Missing embedding_weights %s." % embedding_weights)

  dtype = sparse_weights.dtype if sparse_weights is not None else None
  embedding_weights = [
      w if (isinstance(w, resource_variable_ops.ResourceVariable)
            and dtype in (None, w.dtype))
      else ops.convert_to_tensor(w, dtype=dtype)
      for w in embedding_weights
  ]

  with ops.name_scope(name, "embedding_lookup", embedding_weights +
                      [sparse_ids, sparse_weights]) as scope:
    # Reshape higher-rank sparse ids and weights to linear segment ids.
    original_shape = sparse_ids.dense_shape
    original_rank_dim = tensor_shape.dimension_value(
        sparse_ids.dense_shape.get_shape()[0])
    original_rank = (
        array_ops.size(original_shape)
        if original_rank_dim is None else original_rank_dim)
    sparse_ids = sparse_ops.sparse_reshape(sparse_ids, [
        math_ops.reduce_prod(
            array_ops.slice(original_shape, [0], [original_rank - 1])),
        array_ops.gather(original_shape, original_rank - 1)
    ])
    if sparse_weights is not None:
      sparse_weights = sparse_tensor.SparseTensor(sparse_ids.indices,
                                                  sparse_weights.values,
                                                  sparse_ids.dense_shape)

    # Prune invalid ids and weights.
    sparse_ids, sparse_weights = _prune_invalid_ids(sparse_ids, sparse_weights)
    if combiner != "sum":
      sparse_ids, sparse_weights = _prune_invalid_weights(
          sparse_ids, sparse_weights)

    # Fill in dummy values for empty features, if necessary.
    sparse_ids, is_row_empty = sparse_ops.sparse_fill_empty_rows(
        sparse_ids, default_id or 0)
    if sparse_weights is not None:
      sparse_weights, _ = sparse_ops.sparse_fill_empty_rows(sparse_weights, 1.0)

    result = embedding_lookup_sparse(
        embedding_weights,
        sparse_ids,
        sparse_weights,
        combiner=combiner,
        partition_strategy=partition_strategy,
        name=None if default_id is None else scope,
        max_norm=max_norm)

    if default_id is None:
      # Broadcast is_row_empty to the same shape as embedding_lookup_result,
      # for use in Select.
      is_row_empty = array_ops.tile(
          array_ops.reshape(is_row_empty, [-1, 1]),
          array_ops.stack([1, array_ops.shape(result)[1]]))

      result = array_ops.where(
          is_row_empty, array_ops.zeros_like(result), result, name=scope)

    # Reshape back from linear ids back into higher-dimensional dense result.
    final_result = array_ops.reshape(
        result,
        array_ops.concat([
            array_ops.slice(
                math_ops.cast(original_shape, dtypes.int32), [0],
                [original_rank - 1]),
            array_ops.slice(array_ops.shape(result), [1], [-1])
        ], 0))
    final_result.set_shape(
        tensor_shape.unknown_shape(
            (tensor_shape.Dimension(original_rank_dim) - 1).value).concatenate(
                result.get_shape()[1:]))
    return final_result


def embedding_lookup_ragged(embedding_weights,
                            ragged_ids,
                            partition_strategy="mod",
                            max_norm=None,
                            name=None):
  """Look up the ragged ids in a list of embedding tensors.

  Args:
    embedding_weights: A tensor representing the complete embedding tensor
      having the shape [e1, ...eM]
    ragged_ids: A 'RaggedTensor' with type 'int32' or 'int64' containing the ids
      to be looked up in 'embedding_weights' of shape [r0, ..rN]. Values must be
      in the range '[0, embedding_weights.shape[0]]'.
    partition_strategy: A string specifying the partitioning strategy.
    max_norm: If not `None`, each embedding is clipped if its l2-norm is larger
      than this value.
    name: A name for the operation (optional)

  Returns:
    A ragged tensor of shape [r0, r1, ...rN, e1, ...eM].

  Raises:
    ValueError: whether the embedding_weights is empty or the ragged_ids is
    not a RaggedTensor.
  """
  if embedding_weights is None:
    raise ValueError("The embedding weights must be specified.")
  if isinstance(embedding_weights, (list, tuple)) and not embedding_weights:
    raise ValueError("The embedding weights should not be empty.")
  if ragged_ids.dtype != dtypes.int32 and ragged_ids.dtype != dtypes.int64:
    raise ValueError("The values contained by the inputs have type " +
                     str(ragged_ids.dtype) +
                     " and cannot be processed. All values"
                     " should be indices, either of type `in32` or `int64`.")

  with ops.name_scope(name, "embedding_lookup_ragged") as name:
    looked_up_ragged = ragged_functional_ops.map_flat_values(
        embedding_lookup,
        params=embedding_weights,
        ids=ragged_ids,
        partition_strategy=partition_strategy,
        max_norm=max_norm)

    return looked_up_ragged


def _prune_invalid_ids(sparse_ids, sparse_weights):
  """Prune invalid IDs (< 0) from the input ids and weights."""
  is_id_valid = math_ops.greater_equal(sparse_ids.values, 0)
  if sparse_weights is not None:
    is_id_valid = math_ops.logical_and(
        is_id_valid,
        array_ops.ones_like(sparse_weights.values, dtype=dtypes.bool))
  sparse_ids = sparse_ops.sparse_retain(sparse_ids, is_id_valid)
  if sparse_weights is not None:
    sparse_weights = sparse_ops.sparse_retain(sparse_weights, is_id_valid)
  return sparse_ids, sparse_weights


def _prune_invalid_weights(sparse_ids, sparse_weights):
  """Prune invalid weights (< 0) from the input ids and weights."""
  if sparse_weights is not None:
    is_weights_valid = math_ops.greater(sparse_weights.values, 0)
    sparse_ids = sparse_ops.sparse_retain(sparse_ids, is_weights_valid)
    sparse_weights = sparse_ops.sparse_retain(sparse_weights, is_weights_valid)
  return sparse_ids, sparse_weights