我有一个模型，它带有三个带有相同标签的可变长度输入。我有办法以某种方式使用pack_padded_sequence吗？如果是这样，我该如何对序列进行排序？
例如，
a = (([0,1,2], [3,4], [5,6,7,8]), 1) # training data is in length 3,2,4; label is 1
b = (([0,1], [2], [6,7,8,9,10]), 1)
a和b都将被输入三个独立的LSTM，结果将被合并以预测目标。
答案 0 :(得分：8)
让我们一步一步来做。
输入数据处理
a = (([0,1,2], [3,4], [5,6,7,8]), 1)
# store length of each element in an array
len_a = np.array([len(a) for a in a[0]])
variable_a = np.zeros((len(len_a), np.amax(len_a)))
for i, a in enumerate(a[0]):
variable_a[i, 0:len(a)] = a
vocab_size = len(np.unique(variable_a))
Variable(torch.from_numpy(variable_a).long())
print(variable_a)
打印：
Variable containing:
0 1 2 0
3 4 0 0
5 6 7 8
[torch.DoubleTensor of size 3x4]
定义嵌入和RNN层
现在，让我们说，我们有一个嵌入和RNN图层类如下。
class EmbeddingLayer(nn.Module):
def __init__(self, input_size, emsize):
super(EmbeddingLayer, self).__init__()
self.embedding = nn.Embedding(input_size, emsize)
def forward(self, input_variable):
return self.embedding(input_variable)
class Encoder(nn.Module):
def __init__(self, input_size, hidden_size, bidirection):
super(Encoder, self).__init__()
self.input_size = input_size
self.hidden_size = hidden_size
self.bidirection = bidirection
self.rnn = nn.LSTM(self.input_size, self.hidden_size, batch_first=True,
bidirectional=self.bidirection)
def forward(self, sent_variable, sent_len):
# Sort by length (keep idx)
sent_len, idx_sort = np.sort(sent_len)[::-1], np.argsort(-sent_len)
idx_unsort = np.argsort(idx_sort)
idx_sort = torch.from_numpy(idx_sort)
sent_variable = sent_variable.index_select(0, Variable(idx_sort))
# Handling padding in Recurrent Networks
sent_packed = nn.utils.rnn.pack_padded_sequence(sent_variable, sent_len, batch_first=True)
sent_output = self.rnn(sent_packed)[0]
sent_output = nn.utils.rnn.pad_packed_sequence(sent_output, batch_first=True)[0]
# Un-sort by length
idx_unsort = torch.from_numpy(idx_unsort)
sent_output = sent_output.index_select(0, Variable(idx_unsort))
return sent_output
嵌入并编码已处理的输入数据
我们可以按如下方式嵌入和编码输入。
emb = EmbeddingLayer(vocab_size, 50)
enc = Encoder(50, 100, False, 'LSTM')
emb_a = emb(variable_a)
enc_a = enc(emb_a, len_a)
如果您打印enc_a的尺寸，则会获得torch.Size([3, 4, 100])。我希望你理解这种形状的含义。
请注意，上述代码仅在CPU上运行。
答案 1 :(得分：0)
以上答案已经非常有用。虽然我经常发现自己在理解pytorch的文档时遇到问题。我创建了这两个功能来帮助我进行包装填充垫包装的思考。
def batch_to_sequence(x, len_x, batch_first):
"""helpful function to do the pack padding shit
returns the pack_padded sequence, whatever that is.
The data does NOT have to be sorted by sentence lenght, we do that for you!
Input:
x: (torch.tensor[max_len, batch, embedding_dim]) tensor containing the
padded data. It expects the embeddings of the words in the sequence
they happen in the sentence. If batch_first == True, then the
max_len and batch dimensions are transposed.
len_x: (torch.tensor[batch]) a tensor containing the length of each
sentence in x.
batch_first: (bool), indicates whether batch or sentence lenght are
indexed in the first dimension of the tensor.
Output:
x: (torch pack padded sequence) a the pad packed sequence containing
the data. (The documentation is horrible, I don't know what a
pack padded sequence really is.)
idx: (torch.tensor[batch]), the indexes used to sort x, this index in
necessary in sequence_to_batch.
len_x: (torch.tensor[batch]) the sorted lenghs, also needed for
sequence_to_batch."""
#sort data because pack_padded is too stupid to do it itself
len_x, idx = len_x.sort(0, descending=True)
x = x[:,idx]
#remove paddings before feeding it to the LSTM
x = torch.nn.utils.rnn.pack_padded_sequence(x,
len_x,
batch_first = batch_first)
return x, len_x, idx
和
def sequence_to_batch(x, len_x, idx, output_size, batch_first, all_hidden = False):
"""helpful function for the pad packed shit.
Input:
x: (packed pad sequence) the ouptut of lstm or pack_padded_sequence().
len_x (torch.tensor[batch]), the sorted leghths that come out of
batch_to_sequence().
idx: (torch.tenssor[batch]), the indexes used to sort len_x
output_size: (int), the expected dimension of the output embeddings.
batch_first: (bool), indicates whether batch or sentence lenght are
indexed in the first dimension of the tensor.
all_hidden: (bool), if False returs the last relevant hidden state - it
ignores the hidden states produced by the padding. If True, returs
all hidden states.
Output:
x: (torch.tensor[batch, embedding_dim]) tensor containing the
padded data.
"""
#re-introduce the paddings
#doc pack_padded_sequence:
#https://pytorch.org/docs/master/nn.html#torch.nn.utils.rnn.pack_padded_sequence
x, _ = torch.nn.utils.rnn.pad_packed_sequence(x,
batch_first = batch_first)
if all_hidden:
return x
#get the indexes of the last token (where the lstm should stop)
longest_sentence = max(len_x)
#subtracsts -1 to see what happens
last_word = [i*longest_sentence + len_x[i] for i in range(len(len_x))]
#get the relevant hidden states
x = x.view(-1, output_size)
x = x[last_word,:]
#unsort the batch!
_, idx = idx.sort(0, descending=False)
x = x[idx, :]
return x
您可以在lstm的前向通行证中使用它们
def forward(self, x, len_x):
#convert batch into a packed_pad sequence
x, len_x, idx = batch_to_sequence(x, len_x, self.batch_first)
#run LSTM,
x, (_, _) = self.uni_lstm(x)
#takes the pad_packed_sequence and gives you the embedding vectors
x = sequence_to_batch(x, len_x, idx, self.output_size, self.batch_first)
return x