+2 votes

** torch.cat()** function concatenates tensors in the given dimension. You can use two or more tensors in this function to concatenate them.

torch.cat(tensors, dim=0, *, out=None) → Tensor

You can also use **hstack()** for horizontal stacking and **vstack()** for vertical stacking of tensors.

Here are some examples:

**1. Concatenating 1d tensors**

>>> import torch

>>> a=torch.randn(3)

>>> b=torch.randn(3)

>>> a

tensor([ 0.4886, 0.1983, -1.8426])

>>> b

tensor([-0.5119, 0.6101, 0.9693])>>> torch.cat((a,b))

tensor([ 0.4886, 0.1983, -1.8426, -0.5119, 0.6101, 0.9693])

2. Concatenating 2d tensors

>>> a=torch.randn(2,3)

>>> a

tensor([[-0.1045, 0.5538, -1.8206],

[-0.6275, 1.6419, 0.3089]])

>>> b=torch.randn(2,3)

>>> b

tensor([[ 0.4254, -0.1717, -0.2772],

[-0.1911, -0.9333, -1.3382]])>>> torch.cat((a,b),1) # horizontal concatenation

tensor([[-0.1045, 0.5538, -1.8206, 0.4254, -0.1717, -0.2772],

[-0.6275, 1.6419, 0.3089, -0.1911, -0.9333, -1.3382]])

>>> torch.hstack((a,b))

tensor([[-0.1045, 0.5538, -1.8206, 0.4254, -0.1717, -0.2772],

[-0.6275, 1.6419, 0.3089, -0.1911, -0.9333, -1.3382]])

>>> torch.cat((a,b),0) # vertical concatenation

tensor([[-0.1045, 0.5538, -1.8206],

[-0.6275, 1.6419, 0.3089],

[ 0.4254, -0.1717, -0.2772],

[-0.1911, -0.9333, -1.3382]])

>>> torch.vstack((a,b))

tensor([[-0.1045, 0.5538, -1.8206],

[-0.6275, 1.6419, 0.3089],

[ 0.4254, -0.1717, -0.2772],

[-0.1911, -0.9333, -1.3382]])