torch.nn.utils.rnn.unpad_sequence¶

torch.nn.utils.rnn.unpad_sequence(padded_sequences, lengths, batch_first=False)[source][source]¶

Unpad padded Tensor into a list of variable length Tensors.

unpad_sequence unstacks padded Tensor into a list of variable length Tensors.

Example

>>> from torch.nn.utils.rnn import pad_sequence, unpad_sequence
>>> a = torch.ones(25, 300)
>>> b = torch.ones(22, 300)
>>> c = torch.ones(15, 300)
>>> sequences = [a, b, c]
>>> padded_sequences = pad_sequence(sequences)
>>> lengths = torch.as_tensor([v.size(0) for v in sequences])
>>> unpadded_sequences = unpad_sequence(padded_sequences, lengths)
>>> torch.allclose(sequences[0], unpadded_sequences[0])
True
>>> torch.allclose(sequences[1], unpadded_sequences[1])
True
>>> torch.allclose(sequences[2], unpadded_sequences[2])
True

Parameters

• padded_sequences (Tensor) – padded sequences.

• lengths (Tensor) – length of original (unpadded) sequences.

• batch_first (bool, optional) – whether batch dimension first or not. Default: False.

Returns

a list of Tensor objects

Return type

list[torch.Tensor]