# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
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# ==============================================================================

"""Wrappers for candidate sampling operations."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from tensorflow.python.framework import random_seed
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import gen_candidate_sampling_ops
from tensorflow.python.ops import math_ops


def uniform_candidate_sampler(true_classes, num_true, num_sampled, unique,
                              range_max, seed=None, name=None):
  """Samples a set of classes using a uniform base distribution.

  This operation randomly samples a tensor of sampled classes
  (`sampled_candidates`) from the range of integers `[0, range_max)`.

  The elements of `sampled_candidates` are drawn without replacement
  (if `unique=True`) or with replacement (if `unique=False`) from
  the base distribution.

  The base distribution for this operation is the uniform distribution
  over the range of integers `[0, range_max)`.

  In addition, this operation returns tensors `true_expected_count`
  and `sampled_expected_count` representing the number of times each
  of the target classes (`true_classes`) and the sampled
  classes (`sampled_candidates`) is expected to occur in an average
  tensor of sampled classes.  These values correspond to `Q(y|x)`
  defined in [this
  document](http://www.tensorflow.org/extras/candidate_sampling.pdf).
  If `unique=True`, then these are post-rejection probabilities and we
  compute them approximately.

  Args:
    true_classes: A `Tensor` of type `int64` and shape `[batch_size,
      num_true]`. The target classes.
    num_true: An `int`.  The number of target classes per training example.
    num_sampled: An `int`.  The number of classes to randomly sample. The
      `sampled_candidates` return value will have shape `[num_sampled]`. If
      `unique=True`, `num_sampled` must be less than or equal to `range_max`.
    unique: A `bool`. Determines whether all sampled classes in a batch are
      unique.
    range_max: An `int`. The number of possible classes.
    seed: An `int`. An operation-specific seed. Default is 0.
    name: A name for the operation (optional).

  Returns:
    sampled_candidates: A tensor of type `int64` and shape `[num_sampled]`.  The
      sampled classes, either with possible duplicates (`unique=False`) or all
      unique (`unique=True`). In either case, `sampled_candidates` is
      independent of the true classes.
    true_expected_count: A tensor of type `float`.  Same shape as
      `true_classes`. The expected counts under the sampling distribution
      of each of `true_classes`.
    sampled_expected_count: A tensor of type `float`. Same shape as
      `sampled_candidates`. The expected counts under the sampling distribution
      of each of `sampled_candidates`.
  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_candidate_sampling_ops._uniform_candidate_sampler(
      true_classes, num_true, num_sampled, unique, range_max, seed=seed1,
      seed2=seed2, name=name)


def log_uniform_candidate_sampler(true_classes, num_true, num_sampled, unique,
                                  range_max, seed=None, name=None):
  """Samples a set of classes using a log-uniform (Zipfian) base distribution.

  This operation randomly samples a tensor of sampled classes
  (`sampled_candidates`) from the range of integers `[0, range_max)`.

  The elements of `sampled_candidates` are drawn without replacement
  (if `unique=True`) or with replacement (if `unique=False`) from
  the base distribution.

  The base distribution for this operation is an approximately log-uniform
  or Zipfian distribution:

  `P(class) = (log(class + 2) - log(class + 1)) / log(range_max + 1)`

  This sampler is useful when the target classes approximately follow such
  a distribution - for example, if the classes represent words in a lexicon
  sorted in decreasing order of frequency. If your classes are not ordered by
  decreasing frequency, do not use this op.

  In addition, this operation returns tensors `true_expected_count`
  and `sampled_expected_count` representing the number of times each
  of the target classes (`true_classes`) and the sampled
  classes (`sampled_candidates`) is expected to occur in an average
  tensor of sampled classes.  These values correspond to `Q(y|x)`
  defined in [this
  document](http://www.tensorflow.org/extras/candidate_sampling.pdf).
  If `unique=True`, then these are post-rejection probabilities and we
  compute them approximately.

  Args:
    true_classes: A `Tensor` of type `int64` and shape `[batch_size,
      num_true]`. The target classes.
    num_true: An `int`.  The number of target classes per training example.
    num_sampled: An `int`.  The number of classes to randomly sample.
    unique: A `bool`. Determines whether all sampled classes in a batch are
      unique.
    range_max: An `int`. The number of possible classes.
    seed: An `int`. An operation-specific seed. Default is 0.
    name: A name for the operation (optional).

  Returns:
    sampled_candidates: A tensor of type `int64` and shape `[num_sampled]`.
      The sampled classes.
    true_expected_count: A tensor of type `float`.  Same shape as
      `true_classes`. The expected counts under the sampling distribution
      of each of `true_classes`.
    sampled_expected_count: A tensor of type `float`. Same shape as
      `sampled_candidates`. The expected counts under the sampling distribution
      of each of `sampled_candidates`.
  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_candidate_sampling_ops._log_uniform_candidate_sampler(
      true_classes, num_true, num_sampled, unique, range_max, seed=seed1,
      seed2=seed2, name=name)


def learned_unigram_candidate_sampler(true_classes, num_true, num_sampled,
                                      unique, range_max, seed=None, name=None):
  """Samples a set of classes from a distribution learned during training.

  This operation randomly samples a tensor of sampled classes
  (`sampled_candidates`) from the range of integers `[0, range_max)`.

  The elements of `sampled_candidates` are drawn without replacement
  (if `unique=True`) or with replacement (if `unique=False`) from
  the base distribution.

  The base distribution for this operation is constructed on the fly
  during training.  It is a unigram distribution over the target
  classes seen so far during training.  Every integer in `[0, range_max)`
  begins with a weight of 1, and is incremented by 1 each time it is
  seen as a target class.  The base distribution is not saved to checkpoints,
  so it is reset when the model is reloaded.

  In addition, this operation returns tensors `true_expected_count`
  and `sampled_expected_count` representing the number of times each
  of the target classes (`true_classes`) and the sampled
  classes (`sampled_candidates`) is expected to occur in an average
  tensor of sampled classes.  These values correspond to `Q(y|x)`
  defined in [this
  document](http://www.tensorflow.org/extras/candidate_sampling.pdf).
  If `unique=True`, then these are post-rejection probabilities and we
  compute them approximately.

  Args:
    true_classes: A `Tensor` of type `int64` and shape `[batch_size,
      num_true]`. The target classes.
    num_true: An `int`.  The number of target classes per training example.
    num_sampled: An `int`.  The number of classes to randomly sample.
    unique: A `bool`. Determines whether all sampled classes in a batch are
      unique.
    range_max: An `int`. The number of possible classes.
    seed: An `int`. An operation-specific seed. Default is 0.
    name: A name for the operation (optional).

  Returns:
    sampled_candidates: A tensor of type `int64` and shape `[num_sampled]`.
      The sampled classes.
    true_expected_count: A tensor of type `float`.  Same shape as
      `true_classes`. The expected counts under the sampling distribution
      of each of `true_classes`.
    sampled_expected_count: A tensor of type `float`. Same shape as
      `sampled_candidates`. The expected counts under the sampling distribution
      of each of `sampled_candidates`.

  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_candidate_sampling_ops._learned_unigram_candidate_sampler(
      true_classes, num_true, num_sampled, unique, range_max, seed=seed1,
      seed2=seed2, name=name)


def fixed_unigram_candidate_sampler(true_classes,
                                    num_true,
                                    num_sampled,
                                    unique,
                                    range_max,
                                    vocab_file='',
                                    distortion=1.0,
                                    num_reserved_ids=0,
                                    num_shards=1,
                                    shard=0,
                                    unigrams=(),
                                    seed=None,
                                    name=None):
  """Samples a set of classes using the provided (fixed) base distribution.

  This operation randomly samples a tensor of sampled classes
  (`sampled_candidates`) from the range of integers `[0, range_max)`.

  The elements of `sampled_candidates` are drawn without replacement
  (if `unique=True`) or with replacement (if `unique=False`) from
  the base distribution.

  The base distribution is read from a file or passed in as an
  in-memory array. There is also an option to skew the distribution by
  applying a distortion power to the weights.

  In addition, this operation returns tensors `true_expected_count`
  and `sampled_expected_count` representing the number of times each
  of the target classes (`true_classes`) and the sampled
  classes (`sampled_candidates`) is expected to occur in an average
  tensor of sampled classes.  These values correspond to `Q(y|x)`
  defined in [this
  document](http://www.tensorflow.org/extras/candidate_sampling.pdf).
  If `unique=True`, then these are post-rejection probabilities and we
  compute them approximately.

  Args:
    true_classes: A `Tensor` of type `int64` and shape `[batch_size,
      num_true]`. The target classes.
    num_true: An `int`.  The number of target classes per training example.
    num_sampled: An `int`.  The number of classes to randomly sample.
    unique: A `bool`. Determines whether all sampled classes in a batch are
      unique.
    range_max: An `int`. The number of possible classes.
    vocab_file: Each valid line in this file (which should have a CSV-like
      format) corresponds to a valid word ID. IDs are in sequential order,
      starting from num_reserved_ids. The last entry in each line is expected
      to be a value corresponding to the count or relative probability. Exactly
      one of `vocab_file` and `unigrams` needs to be passed to this operation.
    distortion: The distortion is used to skew the unigram probability
      distribution.  Each weight is first raised to the distortion's power
      before adding to the internal unigram distribution. As a result,
      `distortion = 1.0` gives regular unigram sampling (as defined by the vocab
      file), and `distortion = 0.0` gives a uniform distribution.
    num_reserved_ids: Optionally some reserved IDs can be added in the range
      `[0, num_reserved_ids]` by the users. One use case is that a special
      unknown word token is used as ID 0. These IDs will have a sampling
      probability of 0.
    num_shards: A sampler can be used to sample from a subset of the original
      range in order to speed up the whole computation through parallelism. This
      parameter (together with `shard`) indicates the number of partitions that
      are being used in the overall computation.
    shard: A sampler can be used to sample from a subset of the original range
      in order to speed up the whole computation through parallelism. This
      parameter (together with `num_shards`) indicates the particular partition
      number of the operation, when partitioning is being used.
    unigrams: A list of unigram counts or probabilities, one per ID in
      sequential order. Exactly one of `vocab_file` and `unigrams` should be
      passed to this operation.
    seed: An `int`. An operation-specific seed. Default is 0.
    name: A name for the operation (optional).

  Returns:
    sampled_candidates: A tensor of type `int64` and shape `[num_sampled]`.
      The sampled classes.
    true_expected_count: A tensor of type `float`.  Same shape as
      `true_classes`. The expected counts under the sampling distribution
      of each of `true_classes`.
    sampled_expected_count: A tensor of type `float`. Same shape as
      `sampled_candidates`. The expected counts under the sampling distribution
      of each of `sampled_candidates`.

  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_candidate_sampling_ops._fixed_unigram_candidate_sampler(
      true_classes, num_true, num_sampled, unique, range_max,
      vocab_file=vocab_file, distortion=distortion,
      num_reserved_ids=num_reserved_ids, num_shards=num_shards, shard=shard,
      unigrams=unigrams, seed=seed1, seed2=seed2, name=name)


def all_candidate_sampler(true_classes, num_true, num_sampled, unique,
                          seed=None, name=None):
  """Generate the set of all classes.

  Deterministically generates and returns the set of all possible classes.
  For testing purposes.  There is no need to use this, since you might as
  well use full softmax or full logistic regression.

  Args:
    true_classes: A `Tensor` of type `int64` and shape `[batch_size,
      num_true]`. The target classes.
    num_true: An `int`.  The number of target classes per training example.
    num_sampled: An `int`.  The number of possible classes.
    unique: A `bool`. Ignored.
      unique.
    seed: An `int`. An operation-specific seed. Default is 0.
    name: A name for the operation (optional).

  Returns:
    sampled_candidates: A tensor of type `int64` and shape `[num_sampled]`.
      This operation deterministically returns the entire range
      `[0, num_sampled]`.
    true_expected_count: A tensor of type `float`.  Same shape as
      `true_classes`. The expected counts under the sampling distribution
      of each of `true_classes`. All returned values are 1.0.
    sampled_expected_count: A tensor of type `float`. Same shape as
      `sampled_candidates`. The expected counts under the sampling distribution
      of each of `sampled_candidates`. All returned values are 1.0.
  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_candidate_sampling_ops._all_candidate_sampler(
      true_classes, num_true, num_sampled, unique, seed=seed1, seed2=seed2,
      name=name)


def compute_accidental_hits(true_classes, sampled_candidates, num_true,
                            seed=None, name=None):
  """Compute the position ids in `sampled_candidates` matching `true_classes`.

  In Candidate Sampling, this operation facilitates virtually removing
  sampled classes which happen to match target classes.  This is done
  in Sampled Softmax and Sampled Logistic.

  See our [Candidate Sampling Algorithms
  Reference](http://www.tensorflow.org/extras/candidate_sampling.pdf).

  We presuppose that the `sampled_candidates` are unique.

  We call it an 'accidental hit' when one of the target classes
  matches one of the sampled classes.  This operation reports
  accidental hits as triples `(index, id, weight)`, where `index`
  represents the row number in `true_classes`, `id` represents the
  position in `sampled_candidates`, and weight is `-FLOAT_MAX`.

  The result of this op should be passed through a `sparse_to_dense`
  operation, then added to the logits of the sampled classes. This
  removes the contradictory effect of accidentally sampling the true
  target classes as noise classes for the same example.

  Args:
    true_classes: A `Tensor` of type `int64` and shape `[batch_size,
      num_true]`. The target classes.
    sampled_candidates: A tensor of type `int64` and shape `[num_sampled]`.
      The sampled_candidates output of CandidateSampler.
    num_true: An `int`.  The number of target classes per training example.
    seed: An `int`. An operation-specific seed. Default is 0.
    name: A name for the operation (optional).

  Returns:
    indices: A `Tensor` of type `int32` and shape `[num_accidental_hits]`.
      Values indicate rows in `true_classes`.
    ids: A `Tensor` of type `int64` and shape `[num_accidental_hits]`.
      Values indicate positions in `sampled_candidates`.
    weights: A `Tensor` of type `float` and shape `[num_accidental_hits]`.
      Each value is `-FLOAT_MAX`.

  """
  seed1, seed2 = random_seed.get_seed(seed)
  return gen_candidate_sampling_ops._compute_accidental_hits(
      true_classes, sampled_candidates, num_true, seed=seed1, seed2=seed2,
      name=name)
