skip-gram word2vec代码实现

2013年，《Distributed Representations of Words and Phrases and their Compositionality》提出训练词向量模型Word2vec的方法，即CBOW和Skip-gram。CBOW是根据上下文词预测中心词，Skip-gram是根据中心词预测周围词。相对来说Skip-gram训练出的Word2vec模型较好，可以参考word2vec中cbow 与 skip-gram的比较。

1. Skip-gram

Skip-gram方法利用神经网络模型，分成输入层，隐层，输出层，在隐层没有使用激活函数，只有线性函数，模型结构如图所示，具体代码实现如下所示。

2. 代码实现

import numpy as np
import torch
import torch.nn as nn
import torch.optim as optim
import matplotlib.pyplot as plt

#skip-gram word2vec
class Word2Vec(nn.Module):
    def __init__(self,vocab_size,embedding_size):
        super(Word2Vec, self).__init__()
        self.W = nn.Linear(vocab_size, embedding_size, bias=False) # vocab_size：词表大小，embedding_size:维度大小
        self.WT = nn.Linear(embedding_size, vocab_size, bias=False) 

    def forward(self, X):
        # X : [batch_size, voc_size]
        hidden_layer = self.W(X) # 隐层 : [batch_size, embedding_size]  线性层
        output_layer = self.WT(hidden_layer) # 输出层 : [batch_size, voc_size]  输出层
        return output_layer

#随机选择训练数据
def random_batch(skip_grams, batch_size, vocab_size):
    random_inputs = []
    random_labels = []
    random_index = np.random.choice(range(len(skip_grams)), batch_size, replace=False)

    for i in random_index:
        random_inputs.append(np.eye(vocab_size)[skip_grams[i][0]])  # target
        random_labels.append(skip_grams[i][1]) 
    return random_inputs, random_labels

#生成skip-gram
def skip_grams_fun(sentences,word_dict):
    skip_grams = []
    word_sequence = " ".join(sentences).split()
    for i in range(1, len(word_sequence) - 1):
        target = word_dict[word_sequence[i]]
        context = [word_dict[word_sequence[i - 1]], word_dict[word_sequence[i + 1]]]
        for w in context:
            skip_grams.append([target, w])
    return skip_grams

if __name__ == '__main__':
    batch_size = 2  #批量大小
    embedding_size = 2  #向量维度大小
    #文本
    sentences = ["apple banana fruit", "banana orange fruit", "orange banana fruit",
                 "dog cat animal", "cat monkey animal", "monkey dog animal"]

    word_sequence = " ".join(sentences).split()
    word_list = " ".join(sentences).split()
    word_list = list(set(word_list))
    word_dict = {w: i for i, w in enumerate(word_list)}  #词典
    vocab_size = len(word_list)  #词典大小
    skip_grams = []
    skip_grams1 = skip_grams_fun(sentences[:3],word_dict)
    skip_grams2 = skip_grams_fun(sentences[3:],word_dict)
    skip_grams.extend(skip_grams1)
    skip_grams.extend(skip_grams2)

    model = Word2Vec(vocab_size,embedding_size)  
    criterion = nn.CrossEntropyLoss()   #交叉熵损失
    optimizer = optim.Adam(model.parameters(), lr=0.001)  #优化器

    for epoch in range(10000):
        input_batch, target_batch = random_batch(skip_grams, batch_size, vocab_size)
        input_batch = torch.Tensor(input_batch)  #类型转换
        target_batch = torch.LongTensor(target_batch)

        optimizer.zero_grad()
        output = model(input_batch)  # 输出 : [batch_size, voc_size]
        loss = criterion(output, target_batch)
        if (epoch + 1) % 1000 == 0:
            print('Epoch:', '%04d' % (epoch + 1), 'cost =', '{:.6f}'.format(loss))
        loss.backward()
        optimizer.step()

    for i, label in enumerate(word_list):
        W, WT = model.parameters()  
        x, y = W[0][i].item(), W[1][i].item()
        plt.scatter(x, y)
        plt.annotate(label, xy=(x, y), xytext=(5, 2), textcoords='offset points', ha='right', va='bottom')
    plt.show()

Word2vec模型在自然语言处理领域会经常用到，通常会使用已封装好的包，若想了解具体实现方式，可以阅读上述代码实现或者原文，否则一般使用gensim，使用方便，作者也会使用gensim训练word2vec。