tf.TensorArray

Class wrapping dynamic-sized, per-time-step, write-once Tensor arrays.

Used in the notebooks

Used in the guide Used in the tutorials

This class is meant to be used with dynamic iteration primitives such as while_loop and map_fn. It supports gradient back-propagation via special "flow" control flow dependencies.

Example 1: Plain reading and writing.

ta = tf.TensorArray(tf.float32, size=0, dynamic_size=True, clear_after_read=False)
ta = ta.write(0, 10)
ta = ta.write(1, 20)
ta = ta.write(2, 30)

ta.read(0)
<tf.Tensor: shape=(), dtype=float32, numpy=10.0>
ta.read(1)
<tf.Tensor: shape=(), dtype=float32, numpy=20.0>
ta.read(2)
<tf.Tensor: shape=(), dtype=float32, numpy=30.0>
ta.stack()
<tf.Tensor: shape=(3,), dtype=float32, numpy=array([10., 20., 30.],
dtype=float32)>

Example 2: Fibonacci sequence algorithm that writes in a loop then returns.

@tf.function
def fibonacci(n):
  ta = tf.TensorArray(tf.float32, size=0, dynamic_size=True)
  ta = ta.unstack([0., 1.])

  for i in range(2, n):
    ta = ta.write(i, ta.read(i - 1) + ta.read(i - 2))

  return ta.stack()

fibonacci(7)
<tf.Tensor: shape=(7,), dtype=float32,
numpy=array([0., 1., 1., 2., 3., 5., 8.], dtype=float32)>

Example 3: A simple loop interacting with a tf.Variable.

v = tf.Variable(1)
@tf.function
def f(x):
  ta = tf.TensorArray(tf.int32, size=0, dynamic_size=True)
  for i in tf.range(x):
    v.assign_add(i)
    ta = ta.write(i, v)
  return ta.stack()
f(5)
<tf.Tensor: shape=(5,), dtype=int32, numpy=array([ 1,  2,  4,  7, 11],
dtype=int32)>

dtype (required) data type of the TensorArray.
size (optional) int32 scalar Tensor: the size of the TensorArray. Required if handle is not provided.
dynamic_size (optional) Python bool: If true, writes to the TensorArray can grow the TensorArray past its initial size. Default: False.
clear_after_read Boolean (optional, default: True). If True, clear TensorArray values after reading them. This disables read-many semantics, but allows early release of memory.
tensor_array_name (optional) Python string: the name of the TensorArray. This is used when creating the TensorArray handle. If this value is set, handle should be None.
handle (optional) A Tensor handle to an existing TensorArray. If this is set, tensor_array_name should be None. Only supported in graph mode.
flow (optional) A float Tensor scalar coming from an existing TensorArray.flow. Only supported in graph mode.
infer_shape (optional, default: True) If True, shape inference is enabled. In this case, all elements must have the same shape.
element_shape (optional, default: None) A TensorShape object specifying the shape constraints of each of the elements of the TensorArray. Need not be fully defined.
colocate_with_first_write_call If True, the TensorArray will be colocated on the same device as the Tensor used on its first write (write operations include write, unstack, and split). If False, the TensorArray will be placed on the device determined by the device context available during its initialization.
name A name for the operation (optional).

ValueError if both handle and tensor_array_name are provided.
TypeError if handle is provided but is not a Tensor.

dtype The data type of this TensorArray.
dynamic_size Python bool; if True the TensorArray can grow dynamically.
element_shape The tf.TensorShape of elements in this TensorArray.
flow The flow Tensor forcing ops leading to this TensorArray state.
handle The reference to the TensorArray.

Methods

close

View source

Close the current TensorArray.

concat

View source

Return the values in the TensorArray as a concatenated Tensor.

All of the values must have been written, their ranks must match, and and their shapes must all match for all dimensions except the first.

Args
name A name for the operation (optional).

Returns
All the tensors in the TensorArray concatenated into one tensor.

gather

View source

Return selected values in the TensorArray as a packed Tensor.

All of selected values must have been written and their shapes must all match.

Args
indices A 1-D Tensor taking values in [0, max_value). If the TensorArray is not dynamic, max_value=size().
name A name for the operation (optional).

Returns
The tensors in the TensorArray selected by indices, packed into one tensor.

grad

View source

identity

View source

Returns a TensorArray with the same content and properties.

Returns
A new TensorArray object with flow that ensures the control dependencies from the contexts will become control dependencies for writes, reads, etc. Use this object for all subsequent operations.

read