深度有趣 | 24 语句类似度计算

简介

使用Keras实现Siamese Network并进行语句类似度的计算

原理

Siamese Network是指网络中包含两个或以上彻底相同的子网络，多应用于语句类似度计算、人脸匹配、签名鉴别等任务上

• 语句类似度计算：输入两句话，判断是不是一个意思
• 人脸匹配：输入两张人脸，判断是不是同一我的
• 签名鉴别：输入两个签名，判断是不是同一我的所写

以语句类似度计算为例，两边的子网络从Embedding层到LSTM层等都是彻底相同的，整个模型称做MaLSTM（Manhattan LSTM）

经过LSTM层的最后输出获得两句话的固定长度表示，再使用如下公式计算二者的类似度，类似度在0至1之间

$$ D=\exp{(-\left| h^{(left)}-h^{(right)} \right|_1)} $$

数据

使用Kaggle上的Quora问题对数据，Quora对应外国的知乎，https://www.kaggle.com/c/quora-question-pairs

训练集和测试集分别有404290和3563475条数据，每条数据包括如下字段，但测试集不包括is_duplicate字段

• id：问题对的id
• qid1：问题1的id
• qid2：问题2的id
• question1：问题1的文本
• question2：问题2的文本
• is_duplicate：两个问题是否是意思同样，0或1

实现

加载库

# -*- coding: utf-8 -*-

from keras.preprocessing.sequence import pad_sequences
from keras.models import Model
from keras.layers import Input, Embedding, LSTM, Lambda
import keras.backend as K
from keras.optimizers import Adam

import pandas as pd
import numpy as np
from gensim.models import KeyedVectors
from nltk.corpus import stopwords
from sklearn.model_selection import train_test_split
import matplotlib.pyplot as plt
%matplotlib inline
import re
from tqdm import tqdm
import pickle

加载训练集和测试集

train_df = pd.read_csv('train.csv')
test_df = pd.read_csv('test.csv')
print(len(train_df), len(test_df))
train_df.head()

加载nltk（Natural Language Toolkit）中的停用词，并定义一个文本预处理函数

# 若是报错nltk没有stopwords则下载
# import nltk
# nltk.download('stopwords')

stops = set(stopwords.words('english'))

def preprocess(text):
    # input: 'Hello are you ok?'
    # output: ['Hello', 'are', 'you', 'ok', '?']
    text = str(text)
    text = text.lower()
    
    text = re.sub(r"[^A-Za-z0-9^,!.\/'+-=]", " ", text)  # 去掉其余符号
    text = re.sub(r"what's", "what is ", text)           # 缩写
    text = re.sub(r"\'s", " is ", text)                  # 缩写   
    text = re.sub(r"\'ve", " have ", text)               # 缩写
    text = re.sub(r"can't", "cannot ", text)             # 缩写
    text = re.sub(r"n't", " not ", text)                 # 缩写
    text = re.sub(r"i'm", "i am ", text)                 # 缩写
    text = re.sub(r"\'re", " are ", text)                # 缩写
    text = re.sub(r"\'d", " would ", text)               # 缩写
    text = re.sub(r"\'ll", " will ", text)               # 缩写
    text = re.sub(r",", " ", text)                       # 去除逗号
    text = re.sub(r"\.", " ", text)                      # 去除句号
    text = re.sub(r"!", " ! ", text)                     # 保留感叹号
    text = re.sub(r"\/", " ", text)                      # 去掉右斜杠
    text = re.sub(r"\^", " ^ ", text)                    # 其余符号
    text = re.sub(r"\+", " + ", text)                    # 其余符号
    text = re.sub(r"\-", " - ", text)                    # 其余符号
    text = re.sub(r"\=", " = ", text)                    # 其余符号
    text = re.sub(r"\'", " ", text)                      # 去掉单引号 
    text = re.sub(r"(\d+)(k)", r"\g<1>000", text)        # 把30k等替换成30000
    text = re.sub(r":", " : ", text)                     # 其余符号
    text = re.sub(r" e g ", " eg ", text)                # 其余词
    text = re.sub(r" b g ", " bg ", text)                # 其余词
    text = re.sub(r" u s ", " american ", text)          # 其余词
    text = re.sub(r"\0s", "0", text)                     # 其余词
    text = re.sub(r" 9 11 ", " 911 ", text)              # 其余词
    text = re.sub(r"e - mail", "email", text)            # 其余词
    text = re.sub(r"j k", "jk", text)                    # 其余词
    text = re.sub(r"\s{2,}", " ", text)                  # 将多个空白符替换成一个空格

    return text.split()

加载Google预训练好的300维词向量

word2vec = KeyedVectors.load_word2vec_format('GoogleNews-vectors-negative300.bin.gz', binary=True)

整理词典，一共有58564个词，将文本替换成整数序列表示，得到词向量映射矩阵

vocabulary = []
word2id = {}
id2word = {}

for df in [train_df, test_df]:
    for i in tqdm(range(len(df))):
        row = df.iloc[i]
        for column in ['question1', 'question2']:
            q2n = []
            for word in preprocess(row[column]):
                if word in stops or word not in word2vec.vocab:
                    continue
                
                if word not in vocabulary:
                    word2id[word] = len(vocabulary) + 1
                    id2word[len(vocabulary) + 1] = word
                    vocabulary.append(word)
                    q2n.append(word2id[word])
                else:
                    q2n.append(word2id[word])
            
            df.at[i, column] = q2n

embedding_dim = 300
embeddings = np.random.randn(len(vocabulary) + 1, embedding_dim)
embeddings[0] = 0  # 零填充对应的词向量

for index, word in enumerate(vocabulary):
    embeddings[index] = word2vec.word_vec(word)

del word2vec
print(len(vocabulary))

分割训练集和验证集，将整数序列padding到统一长度

maxlen = max(train_df.question1.map(lambda x: len(x)).max(),
             train_df.question2.map(lambda x: len(x)).max(),
             test_df.question1.map(lambda x: len(x)).max(),
             test_df.question2.map(lambda x: len(x)).max())

valid_size = 40000
train_size = len(train_df) - valid_size

X = train_df[['question1', 'question2']]
Y = train_df['is_duplicate']

X_train, X_valid, Y_train, Y_valid = train_test_split(X, Y, test_size=valid_size)
X_train = {'left': X_train.question1.values, 'right': X_train.question2.values}
X_valid = {'left': X_valid.question1.values, 'right': X_valid.question2.values}
Y_train = np.expand_dims(Y_train.values, axis=-1)
Y_valid = np.expand_dims(Y_valid.values, axis=-1)

# 前向填充或截断
X_train['left'] = np.array(pad_sequences(X_train['left'], maxlen=maxlen))
X_train['right'] = np.array(pad_sequences(X_train['right'], maxlen=maxlen))
X_valid['left'] = np.array(pad_sequences(X_valid['left'], maxlen=maxlen))
X_valid['right'] = np.array(pad_sequences(X_valid['right'], maxlen=maxlen))

print(X_train['left'].shape, X_train['right'].shape)
print(X_valid['left'].shape, X_valid['right'].shape)
print(Y_train.shape, Y_valid.shape)

定义模型并训练

hidden_size = 128
gradient_clipping_norm = 1.25
batch_size = 64
epochs = 20

def exponent_neg_manhattan_distance(args):
    left, right = args
    return K.exp(-K.sum(K.abs(left - right), axis=1, keepdims=True))

left_input = Input(shape=(None,), dtype='int32')
right_input = Input(shape=(None,), dtype='int32')

embedding_layer = Embedding(len(embeddings), embedding_dim, weights=[embeddings], input_length=maxlen, trainable=False)

embedded_left = embedding_layer(left_input)
embedded_right = embedding_layer(right_input)

shared_lstm = LSTM(hidden_size)

left_output = shared_lstm(embedded_left)
right_output = shared_lstm(embedded_right)

malstm_distance = Lambda(exponent_neg_manhattan_distance, output_shape=(1,))([left_output, right_output])

malstm = Model([left_input, right_input], malstm_distance)

optimizer = Adam(clipnorm=gradient_clipping_norm)
malstm.compile(loss='mean_squared_error', optimizer=optimizer, metrics=['accuracy'])

history = malstm.fit([X_train['left'], X_train['right']], Y_train, batch_size=batch_size, epochs=epochs,
                     validation_data=([X_valid['left'], X_valid['right']], Y_valid))

绘制训练过程当中的正确率曲线和损失函数曲线

# Plot Accuracy
plt.plot(history.history['acc'])
plt.plot(history.history['val_acc'])
plt.title('Model Accuracy')
plt.ylabel('Accuracy')
plt.xlabel('Epoch')
plt.legend(['Train', 'Validation'], loc='upper left')
plt.show()

# Plot Loss
plt.plot(history.history['loss'])
plt.plot(history.history['val_loss'])
plt.title('Model Loss')
plt.ylabel('Loss')
plt.xlabel('Epoch')
plt.legend(['Train', 'Validation'], loc='upper right')
plt.show()

训练集损失不断下降，但验证集损失趋于平缓，说明模型泛化能力还不够

训练集正确率提高到了86%以上，而验证集正确率维持在80%左右，模型有待进一步改进

保存模型，以便后续使用

malstm.save('malstm.h5')
with open('data.pkl', 'wb') as fw:
    pickle.dump({'word2id': word2id, 'id2word': id2word}, fw)

在单机上使用训练好的模型作个简单测试，从训练集中随机拿出一些样本，观察模型分类的结果是否和标签一致，主要是熟悉下如何应用模型进行推断

# -*- coding: utf-8 -*-

from keras.preprocessing.sequence import pad_sequences
from keras.models import Model, load_model
import pandas as pd
import numpy as np
from nltk.corpus import stopwords
import re
import pickle

with open('data.pkl', 'rb') as fr:
    data = pickle.load(fr)
    word2id = data['word2id']
    id2word = data['id2word']

train_df = pd.read_csv('train.csv')

stops = set(stopwords.words('english'))
def preprocess(text):
    # input: 'Hello are you ok?'
    # output: ['Hello', 'are', 'you', 'ok', '?']
    text = str(text)
    text = text.lower()
    
    text = re.sub(r"[^A-Za-z0-9^,!.\/'+-=]", " ", text)  # 去掉其余符号
    text = re.sub(r"what's", "what is ", text)           # 缩写
    text = re.sub(r"\'s", " is ", text)                  # 缩写   
    text = re.sub(r"\'ve", " have ", text)               # 缩写
    text = re.sub(r"can't", "cannot ", text)             # 缩写
    text = re.sub(r"n't", " not ", text)                 # 缩写
    text = re.sub(r"i'm", "i am ", text)                 # 缩写
    text = re.sub(r"\'re", " are ", text)                # 缩写
    text = re.sub(r"\'d", " would ", text)               # 缩写
    text = re.sub(r"\'ll", " will ", text)               # 缩写
    text = re.sub(r",", " ", text)                       # 去除逗号
    text = re.sub(r"\.", " ", text)                      # 去除句号
    text = re.sub(r"!", " ! ", text)                     # 保留感叹号
    text = re.sub(r"\/", " ", text)                      # 去掉右斜杠
    text = re.sub(r"\^", " ^ ", text)                    # 其余符号
    text = re.sub(r"\+", " + ", text)                    # 其余符号
    text = re.sub(r"\-", " - ", text)                    # 其余符号
    text = re.sub(r"\=", " = ", text)                    # 其余符号
    text = re.sub(r"\'", " ", text)                      # 去掉单引号 
    text = re.sub(r"(\d+)(k)", r"\g<1>000", text)        # 把30k等替换成30000
    text = re.sub(r":", " : ", text)                     # 其余符号
    text = re.sub(r" e g ", " eg ", text)                # 其余词
    text = re.sub(r" b g ", " bg ", text)                # 其余词
    text = re.sub(r" u s ", " american ", text)          # 其余词
    text = re.sub(r"\0s", "0", text)                     # 其余词
    text = re.sub(r" 9 11 ", " 911 ", text)              # 其余词
    text = re.sub(r"e - mail", "email", text)            # 其余词
    text = re.sub(r"j k", "jk", text)                    # 其余词
    text = re.sub(r"\s{2,}", " ", text)                  # 将多个空白符替换成一个空格

    return text.split()

malstm = load_model('malstm.h5')
correct = 0
for i in range(5):
    print('Testing Case:', i + 1)
    random_sample = dict(train_df.iloc[np.random.randint(len(train_df))])
    left = random_sample['question1']
    right = random_sample['question2']
    print('Origin Questions...')
    print('==', left)
    print('==', right)

    left = preprocess(left)
    right = preprocess(right)
    print('Preprocessing...')
    print('==', left)
    print('==', right)

    left = [word2id[w] for w in left if w in word2id]
    right = [word2id[w] for w in right if w in word2id]
    print('To ids...')
    print('==', left, [id2word[i] for i in left])
    print('==', right, [id2word[i] for i in right])

    left = np.expand_dims(left, 0)
    right = np.expand_dims(right, 0)
    maxlen = max(left.shape[-1], right.shape[-1])
    left = pad_sequences(left, maxlen=maxlen)
    right = pad_sequences(right, maxlen=maxlen)

    print('Padding...')
    print('==', left.shape)
    print('==', right.shape)

    pred = malstm.predict([left, right])
    pred = 1 if pred[0][0] > 0.5 else 0
    print('True:', random_sample['is_duplicate'])
    print('Pred:', pred)
    if pred == random_sample['is_duplicate']:
        correct += 1
print(correct / 5)

参考

• How to predict Quora Question Pairs using Siamese Manhattan LSTM：https://github.com/eliorc/Medium/blob/master/MaLSTM.ipynb
• Siamese Recurrent Architectures for Learning Sentence Similarity：http://www.mit.edu/~jonasm/info/MuellerThyagarajan_AAAI16.pdf

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