Defined in tensorflow/python/ops/

See the guides: Layers (contrib) > Higher level ops for building neural network layers, Tensor Transformations > Slicing and Joining

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

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])  # [[1, 4], [2, 5], [3, 6]] (Pack along first dim.)
tf.stack([x, y, z], axis=1)  # [[1, 2, 3], [4, 5, 6]]

This is the opposite of unstack. The numpy equivalent is

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


  • 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).


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


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