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欢迎fork我的github:https://github.com/zhaoyu611/DeepLearningTutorialForChinese
最近在学习Git,所以正好趁这个机会,把学习到的知识实践一下~ 看完DeepLearning的原理,有了大体的了解,但是对于theano的代码,还是自己撸一遍印象更深 所以照着deeplearning.net上的代码,重新写了一遍,注释部分是原文翻译和自己的理解。 感兴趣的小伙伴可以一起完成这个工作哦~ 有问题欢迎联系我 Email: zhaoyuafeu@gmail.com QQ: 3062984605
本教程中,你将会学到:
从而实现Semantic Parsing / Slot-Filling(自然语言的理解)。
实验代码见github repository。
如果使用本教程,请引用下列文献:
谢谢!
有问题请联系 Grégoire Mesnil (first-add-a-dot-last-add-at-gmail-add-a-dot-com)。我们很乐意收到您的反馈。
Slot-Filling (Spoken Language Understanding)是对给定的句子中每个单词标定标签。这是一个分类问题。
数据集是DARPA的一个小型数据集:ATIS (Airline Travel Information System)。这里的语句例子使用Inside Outside Beginning (IOB)表示 。
input(words) | show | flights | from | Boston | to | New | York | today |
---|---|---|---|---|---|---|---|---|
Output(labels) | O | O | O | B-dept | O | B-arr | I-arr | B-date |
ATIS 包含单词4978个,句子893个,测试集合包含单词56590个,句子9198个(平均句子长度为15)。类的数量(不同的slots)为128,其中包括O标签(NULL)。
在论文 Microsoft Research people,对于只出现一次的单词,标记为,运用同样的方法标记未出现的单词。在论文Ronan Collobert and colleagues中,用数字表示字符串,例如1984表示DIGITDIGITDIGITDIGIT。
我们将训练集合分为训练集和验证集,分别包含80%和20%的训练语句。 Significant performance improvement difference has to be greater than 0.6% in F1 measure at the 95% level due to the small size of the dataset。为了验证效果,实验中定义了三个矩阵:
这里使用conlleval文本验证模型效果。
一个token对应一个单词。ATIS中词汇表对应的每个token都有相应的索引。每个语句是索引的数组(int32)。其次,每个集合(训练集、验证集、测试集)是索引数组的列表。定义python字典将索引映射到单词。
>>> sentence
array([383, 189, 13, 193, 208, 307, 195, 502, 260, 539,
7, 60, 72, 8, 350, 384], dtype=int32)
>>> map(lambda x: index2word[x], sentence)
[‘please‘, ‘find‘, ‘a‘, ‘flight‘, ‘from‘, ‘miami‘, ‘florida‘,
‘to‘, ‘las‘, ‘vegas‘, ‘<UNK>‘, ‘arriving‘, ‘before‘, ‘DIGIT‘, "o‘clock", ‘pm‘]
对于标签,采用同样的方法:
>>> labels
array([126, 126, 126, 126, 126, 48, 50, 126, 78, 123, 81, 126, 15,
14, 89, 89], dtype=int32)
>>> map(lambda x: index2label[x], labels)
[‘O‘, ‘O‘, ‘O‘, ‘O‘, ‘O‘, ‘B-fromloc.city_name‘, ‘B-fromloc.state_name‘,
‘O‘, ‘B-toloc.city_name‘, ‘I-toloc.city_name‘, ‘B-toloc.state_name‘,
‘O‘, ‘B-arrive_time.time_relative‘, ‘B-arrive_time.time‘,
‘I-arrive_time.time‘, ‘I-arrive_time.time‘]
给定语句:索引的数组,窗口大小:1,3,5,…。现在需要将语句中每个词根据文本窗选定该词周围的词。具体实现如下:
def contextwin(l, win):
‘‘‘
win :: int corresponding to the size of the window
given a list of indexes composing a sentence
l :: array containing the word indexes
it will return a list of list of indexes corresponding
to context windows surrounding each word in the sentence
‘‘‘
assert (win % 2) == 1
assert win >= 1
l = list(l)
lpadded = win // 2 * [-1] + l + win // 2 * [-1]
out = [lpadded[i:(i + win)] for i in range(len(l))]
assert len(out) == len(l)
return out
PADDING索引中的-1插在语句的开始/结束位置。
例子如下:
>>> x
array([0, 1, 2, 3, 4], dtype=int32)
>>> contextwin(x, 3)
[[-1, 0, 1],
[ 0, 1, 2],
[ 1, 2, 3],
[ 2, 3, 4],
[ 3, 4,-1]]
>>> contextwin(x, 7)
[[-1, -1, -1, 0, 1, 2, 3],
[-1, -1, 0, 1, 2, 3, 4],
[-1, 0, 1, 2, 3, 4,-1],
[ 0, 1, 2, 3, 4,-1,-1],
[ 1, 2, 3, 4,-1,-1,-1]]
总的来说,输入为一个索引的数组,输出为索引的矩阵。每行是指定单词的文本窗。
将语句转换成文本窗:索引的矩阵,下一步需要将索引转换为词向量。使用Theano。代码如下:
import theano, numpy
from theano import tensor as T
# nv :: size of our vocabulary
# de :: dimension of the embedding space
# cs :: context window size
nv, de, cs = 1000, 50, 5
embeddings = theano.shared(0.2 * numpy.random.uniform(-1.0, 1.0, (nv+1, de)).astype(theano.config.floatX)) # add one for PADDING at the end
idxs = T.imatrix() # as many columns as words in the context window and as many lines as words in the sentence
x = self.emb[idxs].reshape((idxs.shape[0], de*cs))
符号变量x表示矩阵的维度(语句中单词数量,文本窗的长度)。
下面开始编译theano函数:
>>> sample
array([0, 1, 2, 3, 4], dtype=int32)
>>> csample = contextwin(sample, 7)
[[-1, -1, -1, 0, 1, 2, 3],
[-1, -1, 0, 1, 2, 3, 4],
[-1, 0, 1, 2, 3, 4,-1],
[ 0, 1, 2, 3, 4,-1,-1],
[ 1, 2, 3, 4,-1,-1,-1]]
>>> f = theano.function(inputs=[idxs], outputs=x)
>>> f(csample)
array([[-0.08088442, 0.08458307, 0.05064092, ..., 0.06876887,
-0.06648078, -0.15192257],
[-0.08088442, 0.08458307, 0.05064092, ..., 0.11192625,
0.08745284, 0.04381778],
[-0.08088442, 0.08458307, 0.05064092, ..., -0.00937143,
0.10804889, 0.1247109 ],
[ 0.11038255, -0.10563177, -0.18760249, ..., -0.00937143,
0.10804889, 0.1247109 ],
[ 0.18738101, 0.14727569, -0.069544 , ..., -0.00937143,
0.10804889, 0.1247109 ]], dtype=float32)
>>> f(csample).shape
(5, 350)
我们现在得到了文本窗词向量的一个序列(长度为5,表示语句长度),该词向量非常适用循环神经网络。
Elman循环神经网络(E-RNN)的输入为当前输入(t时刻)和之前隐层状态(t-1时刻)。然后重复该步骤。
在之前章节中,我们构造输入为时序结构。在上述矩阵中,第0行表示t=0时刻,第1行表示t=1时刻,如此等等。
E-RNN中需要学习的参数如下:
整个网络的超参数如下:
代码如下:
class RNNSLU(object):
‘‘‘ elman neural net model ‘‘‘
def __init__(self, nh, nc, ne, de, cs):
‘‘‘
nh :: dimension of the hidden layer
nc :: number of classes
ne :: number of word embeddings in the vocabulary
de :: dimension of the word embeddings
cs :: word window context size
‘‘‘
# parameters of the model
self.emb = theano.shared(name=‘embeddings‘,
value=0.2 * numpy.random.uniform(-1.0, 1.0,
(ne+1, de))
# add one for padding at the end
.astype(theano.config.floatX))
self.wx = theano.shared(name=‘wx‘,
value=0.2 * numpy.random.uniform(-1.0, 1.0,
(de * cs, nh))
.astype(theano.config.floatX))
self.wh = theano.shared(name=‘wh‘,
value=0.2 * numpy.random.uniform(-1.0, 1.0,
(nh, nh))
.astype(theano.config.floatX))
self.w = theano.shared(name=‘w‘,
value=0.2 * numpy.random.uniform(-1.0, 1.0,
(nh, nc))
.astype(theano.config.floatX))
self.bh = theano.shared(name=‘bh‘,
value=numpy.zeros(nh,
dtype=theano.config.floatX))
self.b = theano.shared(name=‘b‘,
value=numpy.zeros(nc,
dtype=theano.config.floatX))
self.h0 = theano.shared(name=‘h0‘,
value=numpy.zeros(nh,
dtype=theano.config.floatX))
# bundle
self.params = [self.emb, self.wx, self.wh, self.w,
self.bh, self.b, self.h0]
以下代码构造词矩阵的输入:
idxs = T.imatrix()
x = self.emb[idxs].reshape((idxs.shape[0], de*cs))
y_sentence = T.ivector(‘y_sentence‘) # labels
调用scan函数实现递归,效果很神奇:
def recurrence(x_t, h_tm1):
h_t = T.nnet.sigmoid(T.dot(x_t, self.wx)
+ T.dot(h_tm1, self.wh) + self.bh)
s_t = T.nnet.softmax(T.dot(h_t, self.w) + self.b)
return [h_t, s_t]
[h, s], _ = theano.scan(fn=recurrence,
sequences=x,
outputs_info=[self.h0, None],
n_steps=x.shape[0])
p_y_given_x_sentence = s[:, 0, :]
y_pred = T.argmax(p_y_given_x_sentence, axis=1)
Theano会自动的计算所有梯度用于最大最小化似然概率:
lr = T.scalar(‘lr‘)
sentence_nll = -T.mean(T.log(p_y_given_x_sentence)
[T.arange(x.shape[0]), y_sentence])
sentence_gradients = T.grad(sentence_nll, self.params)
sentence_updates = OrderedDict((p, p - lr*g)
for p, g in
zip(self.params, sentence_gradients))
然后编译函数:
self.classify = theano.function(inputs=[idxs], outputs=y_pred)
self.sentence_train = theano.function(inputs=[idxs, y_sentence, lr],
outputs=sentence_nll,
updates=sentence_updates)
在每次更新之后,需要将词向量正则化:
self.normalize = theano.function(inputs=[],
updates={self.emb:
self.emb /
T.sqrt((self.emb**2)
.sum(axis=1))
.dimshuffle(0, ‘x‘)})
这就是所有的工作!
根据之前定义的函数,你可以比较预测标签和真实标签,并计算相关矩阵。在这个github仓库,封装了conlleval文本。计算关于Inside Outside Beginning (IOB)的矩阵是十分必要的。如果词起始、词中间、词末端预测都是正确的,那么就认为该预测是正确的。需要注意的是,文本后缀是txt,而计算过程中需要将其转换为pl。
对于随机梯度下降法(SGD)的更新,我们将整句作为一个mini-batch,并对每句执行一次更新。对于纯SGD(不同于mini-batch),每个单词执行一次更新。
每次循环/更新之后,需要正则化词向量,保证它们有统一的单位。
在验证集上提前结束是一种常规技术:训练集运行一定的代数,每代在验证集上计算F1得分,并保留最好的模型。
尽管已经有关于超参数选择的研究/代码,这里我们使用KISS随机搜索。
以下参数是一些建议值:
使用download.sh命令下载数据文件后,可以调用以下命令运行程序:
python code/rnnslu.py
(‘NEW BEST: epoch‘, 25, ‘valid F1‘, 96.84, ‘best test F1‘, 93.79)
[learning] epoch 26 >> 100.00% completed in 28.76 (sec) <<
[learning] epoch 27 >> 100.00% completed in 28.76 (sec) <<
...
(‘BEST RESULT: epoch‘, 57, ‘valid F1‘, 97.23, ‘best test F1‘, 94.2, ‘with the model‘, ‘rnnslu‘)
使用github仓库中的代码测试ATIS数据集,每代少于40秒。实验平台为:n i7 CPU 950 @ 3.07GHz using less than 200 Mo of RAM。
[learning] epoch 0 >> 100.00% completed in 34.48 (sec) <<
进行若干代之后,F1得分下降为94.48% 。
NEW BEST: epoch 28 valid F1 96.61 best test F1 94.19
NEW BEST: epoch 29 valid F1 96.63 best test F1 94.42
[learning] epoch 30 >> 100.00% completed in 35.04 (sec) <<
[learning] epoch 31 >> 100.00% completed in 34.80 (sec) <<
[...]
NEW BEST: epoch 40 valid F1 97.25 best test F1 94.34
[learning] epoch 41 >> 100.00% completed in 35.18 (sec) <<
NEW BEST: epoch 42 valid F1 97.33 best test F1 94.48
[learning] epoch 43 >> 100.00% completed in 35.39 (sec) <<
[learning] epoch 44 >> 100.00% completed in 35.31 (sec) <<
[...]
我们可以对学习到的词向量进行K近邻检查。L2距离和cos距离返回结果相同,所以我们画出词向量的cos距离。
atlanta | back | ap80 | but | aircraft | business | a | august | actually | cheap |
---|---|---|---|---|---|---|---|---|---|
phoenix | live | ap57 | if | plane | coach | people | september | provide | weekday |
denver | lives | ap | up | service | first | do | january | prices | weekdays |
tacoma | both | connections | a | airplane | fourth | but | june | stop | am |
columbus | how | tomorrow | now | seating | thrift | numbers | december | number | early |
seattle | me | before | amount | stand | tenth | abbreviation | november | flight | sfo |
minneapolis | out | earliest | more | that | second | if | april | there | milwaukee |
pittsburgh | other | connect | abbreviation | on | fifth | up | july | serving | jfk |
ontario | plane | thrift | restrictions | turboprop | third | serve | jfk | thank | shortest |
montreal | service | coach | mean | mean | twelfth | database | october | ticket | bwi |
philadelphia | fare | today | interested | amount | sixth | passengers | may | are | lastest |
可以看出,较少的词汇表(大约500单词)可以较少计算量。根据人为识别,发现有些分类效果好,有些则较差。
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原文地址:http://blog.csdn.net/zhaoyu106/article/details/52557209