Announcing the TensorFlow Dev Summit 2020 Learn more

tf.stack

TensorFlow 1 version View source on GitHub

Stacks a list of rank-R tensors into one rank-(R+1) tensor.

tf.stack(
    values,
    axis=0,
    name='stack'
)

Used in the guide:

Used in the tutorials:

Packs the list of tensors in values into a tensor with rank one higher than each tensor in values, by packing them along the axis dimension. Given a list of length N of tensors of shape (A, B, C);

if axis == 0 then the output tensor will have the shape (N, A, B, C). if axis == 1 then the output tensor will have the shape (A, N, B, C). Etc.

For example:

x = tf.constant([1, 4]) 
y = tf.constant([2, 5]) 
z = tf.constant([3, 6]) 
tf.stack([x, y, z]) 
<tf.Tensor: shape=(3, 2), dtype=int32, numpy= 
array([[1, 4], 
       [2, 5], 
       [3, 6]], dtype=int32)> 

tf.stack([x, y, z], axis=1)

This is the opposite of unstack. The numpy equivalent is np.stack

np.array_equal(np.stack([x, y, z]), tf.stack([x, y, z])) 
True 

Args:

  • values: A list of Tensor objects with the same shape and type.
  • axis: An int. The axis to stack along. Defaults to the first dimension. Negative values wrap around, so the valid range is [-(R+1), R+1).
  • name: A name for this operation (optional).

Returns:

  • output: A stacked Tensor with the same type as values.

Raises:

  • ValueError: If axis is out of the range [-(R+1), R+1).

Compat aliases