# tensorplay.nn.utils.rnn.pack_padded_sequence

Source: https://www.tensorplay.cn/docs/generated/tensorplay.nn.utils.rnn.pack_padded_sequence.html

```python
tensorplay.nn.utils.rnn.pack_padded_sequence(input: Tensor, lengths, batch_first: bool = False, enforce_sorted: bool = True) → PackedSequence
```

Packs a Tensor containing padded sequences of variable length.

input can be of size T x B x * (if batch_first is False)
or B x T x * (if batch_first is True) where T is the length
of the longest sequence, B is the batch size, and * is any number of dimensions
(including 0).

For unsorted sequences, use enforce_sorted = False. If enforce_sorted is
True, the sequences should be sorted by length in a decreasing order, i.e.
input[:,0] should be the longest sequence, and input[:,B-1] the shortest
one. enforce_sorted = True is only necessary for ONNX export.

It is an inverse operation to [pad_packed_sequence()](/docs/generated/tensorplay.nn.utils.rnn.pad_packed_sequence.html#tensorplay.nn.utils.rnn.pad_packed_sequence), and hence [pad_packed_sequence()](/docs/generated/tensorplay.nn.utils.rnn.pad_packed_sequence.html#tensorplay.nn.utils.rnn.pad_packed_sequence)
can be used to recover the underlying tensor packed in [PackedSequence](/docs/generated/tensorplay.nn.utils.rnn.PackedSequence.html#tensorplay.nn.utils.rnn.PackedSequence).

> **Note**
>
> This function accepts any input that has at least two dimensions. You can apply it to pack the labels, and use the output of the RNN with them to compute the loss directly. A Tensor can be retrieved from a PackedSequence object by accessing its .data attribute.

Parameters:

- input ([Tensor](/docs/generated/tensorplay.Tensor.html#tensorplay.Tensor)) – padded batch of variable length sequences.

- lengths ([Tensor](/docs/generated/tensorplay.Tensor.html#tensorplay.Tensor) or [list](https://docs.python.org/3/builtins/stdtypes.html#list)([int](https://docs.python.org/3/builtins/functions.html#int))) – list of sequence lengths of each batch element (must be on the CPU if provided as a tensor).

- batch_first ([bool](https://docs.python.org/3/builtins/functions.html#bool), optional) – if True, the input is expected in B x T x * format, T x B x * otherwise. Default: False.

- enforce_sorted ([bool](https://docs.python.org/3/builtins/functions.html#bool), optional) – if True, the input is expected to contain sequences sorted by length in a decreasing order. If False, the input will get sorted unconditionally. Default: True.

> **Warning**
>
> The dim of input tensor will be truncated if its length larger than correspond value in length.

Returns:

a [PackedSequence](/docs/generated/tensorplay.nn.utils.rnn.PackedSequence.html#tensorplay.nn.utils.rnn.PackedSequence) object