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tf.RaggedTensor

TensorFlow 2 version View source on GitHub

Represents a ragged tensor.

tf.RaggedTensor(
    values, row_splits, cached_row_lengths=None, cached_value_rowids=None,
    cached_nrows=None, internal=False
)

A RaggedTensor is a tensor with one or more ragged dimensions, which are dimensions whose slices may have different lengths. For example, the inner (column) dimension of rt=[[3, 1, 4, 1], [], [5, 9, 2], [6], []] is ragged, since the column slices (rt[0, :], ..., rt[4, :]) have different lengths. Dimensions whose slices all have the same length are called uniform dimensions. The outermost dimension of a RaggedTensor is always uniform, since it consists of a single slice (and so there is no possibility for differing slice lengths).

The total number of dimensions in a RaggedTensor is called its rank, and the number of ragged dimensions in a RaggedTensor is called its ragged-rank. A RaggedTensor's ragged-rank is fixed at graph creation time: it can't depend on the runtime values of Tensors, and can't vary dynamically for different session runs.

Potentially Ragged Tensors

Many ops support both Tensors and RaggedTensors. The term "potentially ragged tensor" may be used to refer to a tensor that might be either a Tensor or a RaggedTensor. The ragged-rank of a Tensor is zero.

Documenting RaggedTensor Shapes

When documenting the shape of a RaggedTensor, ragged dimensions can be indicated by enclosing them in parentheses. For example, the shape of a 3-D RaggedTensor that stores the fixed-size word embedding for each word in a sentence, for each sentence in a batch, could be written as [num_sentences, (num_words), embedding_size]. The parentheses around (num_words) indicate that dimension is ragged, and that the length of each element list in that dimension may vary for each item.

Component Tensors

Internally, a RaggedTensor consists of a concatenated list of values that are partitioned into variable-length rows. In particular, each RaggedTensor consists of:

  • A values tensor, which concatenates the variable-length rows into a flattened list. For example, the values tensor for [[3, 1, 4, 1], [], [5, 9, 2], [6], []] is [3, 1, 4, 1, 5, 9, 2, 6].

  • A row_splits vector, which indicates how those flattened values are divided into rows. In particular, the values for row rt[i] are stored in the slice rt.values[rt.row_splits[i]:rt.row_splits[i+1]].

Example:

print(tf.RaggedTensor.from_row_splits(
    values=[3, 1, 4, 1, 5, 9, 2, 6],
    row_splits=[0, 4, 4, 7, 8, 8]))
<tf.RaggedTensor [[3, 1, 4, 1], [], [5, 9, 2], [6], []]>

Alternative Row-Partitioning Schemes

In addition to row_splits, ragged tensors provide support for four other row-partitioning schemes:

  • row_lengths: a vector with shape [nrows], which specifies the length of each row.

  • value_rowids and nrows: value_rowids is a vector with shape [nvals], corresponding one-to-one with values, which specifies each value's row index. In particular, the row rt[row] consists of the values rt.values[j] where value_rowids[j]==row. nrows is an integer scalar that specifies the number of rows in the RaggedTensor. (nrows is used to indicate trailing empty rows.)

  • row_starts: a vector with shape [nrows], which specifies the start offset of each row. Equivalent to row_splits[:-1].

  • row_limits: a vector with shape [nrows], which specifies the stop offset of each row. Equivalent to row_splits[1:].

Example: The following ragged tensors are equivalent, and all represent the nested list [[3, 1, 4, 1], [], [5, 9, 2], [6], []].

values = [3, 1, 4, 1, 5, 9, 2, 6]
rt1 = RaggedTensor.from_row_splits(values, row_splits=[0, 4, 4, 7, 8, 8])
rt2 = RaggedTensor.from_row_lengths(values, row_lengths=[4, 0, 3, 1, 0])
rt3 = RaggedTensor.from_value_rowids(
    values, value_rowids=[0, 0, 0, 0, 2, 2, 2, 3], nrows=5)
rt4 = RaggedTensor.from_row_starts(values, row_starts=[0, 4, 4, 7, 8])
rt5 = RaggedTensor.from_row_limits(values, row_limits=[4, 4, 7, 8, 8])

Multiple Ragged Dimensions

RaggedTensors with multiple ragged dimensions can be defined by using a nested RaggedTensor for the values tensor. Each nested RaggedTensor adds a single ragged dimension.

inner_rt = RaggedTensor.from_row_splits(  # =rt1 from above
    values=[3, 1, 4, 1, 5, 9, 2, 6], row_splits=[0, 4, 4, 7, 8, 8])
outer_rt = RaggedTensor.from_row_splits(
    values=inner_rt, row_splits=[0, 3, 3, 5])
print outer_rt.to_list()
[[[3, 1, 4, 1], [], [5, 9, 2]], [], [[6], []]]
print outer_rt.ragged_rank
2

The factory function RaggedTensor.from_nested_row_splits may be used to construct a RaggedTensor with multiple ragged dimensions directly, by providing a list of row_splits tensors:

RaggedTensor.from_nested_row_splits(
    flat_values=[3, 1, 4, 1, 5, 9, 2, 6],
    nested_row_splits=([0, 3, 3, 5], [0, 4, 4, 7, 8, 8])).to_list()
[[[3, 1, 4, 1], [], [5, 9, 2]], [], [[6], []]]

Uniform Inner Dimensions

RaggedTensors with uniform inner dimensions can be defined by using a multidimensional Tensor for values.

rt = RaggedTensor.from_row_splits(values=tf.ones([5, 3]),
..                                    row_splits=[0, 2, 5])
print rt.to_list()
[[[1, 1, 1], [1, 1, 1]],
 [[1, 1, 1], [1, 1, 1], [1, 1, 1]]]
print rt.shape
 (2, ?, 3)

RaggedTensor Shape Restrictions

The shape of a RaggedTensor is currently restricted to have the following form:

  • A single uniform dimension
  • Followed by one or more ragged dimensions
  • Followed by zero or more uniform dimensions.

This restriction follows from the fact that each nested RaggedTensor replaces the uniform outermost dimension of its values with a uniform dimension followed by a ragged dimension.

values A potentially ragged tensor of any dtype and shape [nvals, ...].
row_splits A 1-D integer tensor with shape [nrows+1].
cached_row_lengths A 1-D integer tensor with shape [nrows]
cached_value_rowids A 1-D integer tensor with shape [nvals].
cached_nrows A 1-D integer scalar tensor.
internal True if the constructor is being called by one of the factory methods. If false, an exception will be raised.

TypeError If a row partitioning tensor has an inappropriate dtype.
TypeError If exactly one row partitioning argument was not specified.
ValueError If a row partitioning tensor has an inappropriate shape.
ValueError If multiple partitioning arguments are specified.
ValueError If nrows is specified but value_rowids is not None.

dtype The DType of values in this tensor.
flat_values The innermost values tensor for this ragged tensor.

Concretely, if rt.values is a Tensor, then rt.flat_values is rt.values; otherwise, rt.flat_values is rt.values.flat_values.

Conceptually, flat_values is the tensor formed by flattening the outermost dimension and all of the ragged dimensions into a single dimension.

rt.flat_values.shape = [nvals] + rt.shape[rt.ragged_rank + 1:] (where nvals is the number of items in the flattened dimensions).

Example:

rt = ragged.constant([[[3, 1, 4, 1], [], [5, 9, 2]], [], [[6], []]])
print rt.flat_values()
tf.Tensor([3, 1, 4, 1, 5, 9, 2, 6])

nested_row_splits A tuple containing the row_splits for all ragged dimensions.

rt.nested_row_splits is a tuple containing the row_splits tensors for all ragged dimensions in rt, ordered from outermost to innermost. In particular, rt.nested_row_splits = (rt.row_splits,) + value_splits where:

  • value_splits = () if rt.values is a Tensor.
  • value_splits = rt.values.nested_row_splits otherwise.

Example:

rt = ragged.constant([[[[3, 1, 4, 1], [], [5, 9, 2]], [], [[6], []]]])
for i, splits in enumerate(rt.nested_row_splits()):
  print('Splits for dimension %d: %s' % (i+1, splits))
Splits for dimension 1: [0, 1]
Splits for dimension 2: [0, 3, 3, 5]
Splits for dimension 3: [0, 4, 4, 7, 8, 8]

ragged_rank The number of ragged dimensions in this ragged tensor.
row_splits The row-split indices for this ragged tensor's values.

rt.row_splits specifies where the values for each row begin and end in rt.values. In particular, the values for row rt[i] are stored in the slice rt.values[rt.row_splits[i]:rt.row_splits[i+1]].

Example:

>>> rt = ragged.constant([[3, 1, 4, 1], [], [5, 9, 2], [6], []])
>>> print rt.row_splits  # indices of row splits in rt.values
tf.Tensor([0, 4, 4, 7, 8, 8])

shape The statically known shape of this ragged tensor.
values The concatenated rows for this ragged tensor.

rt.values is a potentially ragged tensor formed by flattening the two outermost dimensions of rt into a single dimension.

rt.values.shape = [nvals] + rt.shape[2:] (where nvals is the number of items in the outer two dimensions of rt).

rt.ragged_rank = self.ragged_rank - 1

Example:

>>> rt = ragged.constant([[3, 1, 4, 1], [], [5, 9, 2], [6], []])
>>> print rt.values
tf.Tensor([3, 1, 4, 1, 5, 9, 2, 6])

Methods

bounding_shape

View source

bounding_shape(
    axis=None, name=None, out_type=None
)

Returns the tight bounding box shape for this RaggedTensor.

Args
axis An integer scalar or vector indicating which axes to return the bounding box for. If not specified, then the full bounding box is returned.
name A name prefix for the returned tensor (optional).
out_type dtype for the returned tensor. Defaults to self.row_splits.dtype.

Returns
An integer Tensor (dtype=self.row_splits.dtype). If axis is not specified, then output is a vector with output.shape=[self.shape.ndims]. If axis is a scalar, then the output is a scalar. If axis is a vector, then output is a vector, where output[i] is the bounding size for dimension axis[i].

Example:

>>> rt = ragged.constant([[1, 2, 3, 4], [5], [], [6, 7, 8, 9], [10]])
>>> rt.bounding_shape()
[5, 4]

consumers

View source

consumers()

from_nested_row_lengths

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@classmethod
from_nested_row_lengths(
    flat_values, nested_row_lengths, name=None, validate=True
)

Creates a RaggedTensor from a nested list of row_lengths tensors.

Equivalent to:

result = flat_values
for row_lengths in reversed(nested_row_lengths):
  result = from_row_lengths(result, row_lengths)

Args
flat_values A potentially ragged tensor.
nested_row_lengths A list of 1-D integer tensors. The ith tensor is used as the row_lengths for the ith ragged dimension.
name A name prefix for the RaggedTensor (optional).
validate If true, then use assertions to check that the arguments form a valid RaggedTensor.

Returns
A RaggedTensor (or flat_values if nested_row_lengths is empty).

from_nested_row_splits

View source

@classmethod
from_nested_row_splits(
    flat_values, nested_row_splits, name=None, validate=True
)

Creates a RaggedTensor from a nested list of row_splits tensors.

Equivalent to:

result = flat_values
for row_splits in reversed(nested_row_splits):
  result = from_row_splits(result, row_splits)

Args
flat_values A potentially ragged tensor.
nested_row_splits A list of 1-D integer tensors. The ith tensor is used as the row_splits for the ith ragged dimension.
name A name prefix for the RaggedTensor (optional).
validate If true, then use assertions to check that the arguments form a valid RaggedTensor.

Returns
A RaggedTensor (or flat_values if nested_row_splits is empty).

from_nested_value_rowids

View source

@classmethod
from_nested_value_rowids(
    flat_values, nested_value_rowids, nested_nrows=None, name=None, validate=True
)

Creates a RaggedTensor from a nested list of value_rowids tensors.

Equivalent to:

result = flat_values
for (rowids, nrows) in reversed(zip(nested_value_rowids, nested_n