基于LSTM的IMDB电影评论情感分析

步骤

加载数据 (50K IMDB Movie Review)
数据清洗
编码“情感”
数据集划分（训练集和测试集）
对评论进行分词和截断/补零操作
构建神经网络模型
训练模型并测试

导入相关工具箱

import pandas as pd    # to load dataset
import numpy as np     # for mathematic equation
import nltk
from nltk.corpus import stopwords   # to get collection of stopwords
from sklearn.model_selection import train_test_split       # for splitting dataset
from tensorflow.keras.preprocessing.text import Tokenizer  # to encode text to int
from tensorflow.keras.preprocessing.sequence import pad_sequences   # to do padding or truncating
from tensorflow.keras.models import Sequential     # the model
from tensorflow.keras.layers import Embedding, LSTM, Dense,Dropout # layers of the architecture
from tensorflow.keras.optimizers import Adam
from tensorflow.keras.callbacks import ModelCheckpoint   # save model
from tensorflow.keras.models import load_model   # load saved model
import re

预览数据集

data = pd.read_csv('IMDB Dataset.csv')print(data)

Stop Word is a commonly used words in a sentence, usually a search engine is programmed to ignore this words (i.e. "the", "a", "an", "of", etc.)

设置停用词，英文中常见的停用词
此处需要下载nltk的stopwords，我选择了百度网盘，直接下载然后放到一个文件夹中D:\nltk_data\corpora

#nltk.download('stopwords')
english_stops = set(stopwords.words('english'))

数据清洗

原始评论数据并不“干净”，存在很多html标签、数字、大写字母、标点符号等等。预处理中需要对评论做预处理，包括去掉html标签，过滤掉停用词，删除标点和数字，将大写字母转成小写

编码正负情感

将正面和负面情感编码成整数，这里0代表负面情感negative，1代表正面情感（positive）

def load_dataset():df = pd.read_csv('IMDB Dataset.csv')x_data = df['review']       # Reviews/Inputy_data = df['sentiment']    # Sentiment/Output# PRE-PROCESS REVIEWx_data = x_data.replace({'<.*?>': ''}, regex = True)          # remove html tagx_data = x_data.replace({'[^A-Za-z]': ' '}, regex = True)     # remove non alphabetx_data = x_data.apply(lambda review: [w for w in review.split() if w not in english_stops])  # remove stop wordsx_data = x_data.apply(lambda review: [w.lower() for w in review])   # lower case# ENCODE SENTIMENT -> 0 & 1y_data = y_data.replace('positive', 1)y_data = y_data.replace('negative', 0)return x_data, y_datax_data, y_data = load_dataset()print('Reviews')
print(x_data, '\n')
print('Sentiment')
print(y_data)

划分数据集

80% 作为训练集
20% 作为测试集
，使用Scikit-Learn中的 train_test_split 方法。

x_train, x_test, y_train, y_test = train_test_split(x_data, y_data, test_size = 0.2)print('Train Set')
print(x_train, '\n')
print(x_test, '\n')
print('Test Set')
print(y_train, '\n')
print(y_test)

该函数能够输出训练集中单条评论最多的词语个数

def get_max_length():review_length = []for review in x_train:review_length.append(len(review))return int(np.ceil(np.mean(review_length)))

分词以及截断和补零

# ENCODE REVIEW
token = Tokenizer(lower=False)    # no need lower, because already lowered the data in load_data()
token.fit_on_texts(x_train)
x_train = token.texts_to_sequences(x_train)
x_test = token.texts_to_sequences(x_test)max_length = get_max_length()
print(max_length)x_train = pad_sequences(x_train, maxlen=max_length, padding='post', truncating='post')
x_test = pad_sequences(x_test, maxlen=max_length, padding='post', truncating='post')total_words = len(token.word_index) + 1   # add 1 because of 0 paddingprint('Encoded X Train\n', x_train, '\n')
print('Encoded X Test\n', x_test, '\n')
print('Maximum review length: ', max_length)

构建深度神经网络模型

Embedding Layer

LSTM Layer

Dense Layer

怎么调参：
EMBED_DIM
LSTM_OUT：LSTM输出维度，可以修改
深度可以改变：增减LSTM层，但是数据较少，过于多的层数会出现过拟合的现象，对于该小实验，不用过多的层数
input_length:输入单词的长度，原本为130，可以设的更小一点
epochs可以改为10，到10次迭代的时候可能收敛。
tf.keras.layers.Bidirectional(tf.keras.layers.LSTM(128, return_sequences=True))：可以修改为双向的LSTM

# ARCHITECTURE
EMBED_DIM =16
LSTM_OUT = 8model = Sequential()
model.add(Embedding(total_words, EMBED_DIM, input_length = max_length))
model.add(LSTM(LSTM_OUT, return_sequences=True))
model.add(LSTM(LSTM_OUT, return_sequences=True))
model.add(LSTM(LSTM_OUT, return_sequences=True))
model.add(LSTM(LSTM_OUT, return_sequences=True))
model.add(LSTM(LSTM_OUT))
model.add(Dropout(0.2))
model.add(Dense(1, activation='sigmoid'))
model.compile(optimizer = Adam(1e-3), loss = 'binary_crossentropy', metrics = ['accuracy'])#metrics分类精度print(model.summary())

训练模型

batch_size 设置为128 ,epochs设置为5

添加 checkpoint当每个epoch训练完成精度有提升时，就更新保存的模型

epoches5轮训练
batch_size每次送入128个进入模型训练，cpu好就可以设置大一些
checkpoint每轮跑完训练好的模型进行保存，save_best_only=true最后只保存精度最高的模型
文件下有一个目录，模型自动存储在models/LSTM.h5，下次可以不用训练了，每次直接调用模型就可以了。

checkpoint = ModelCheckpoint('models/LSTM.h6',monitor='accuracy',save_best_only=True,verbose=1
)model.fit(x_train, y_train, batch_size = 128, epochs = 5, callbacks=[checkpoint])

y_pred = model.predict(x_test, batch_size = 64)
true = 0
for i, y in enumerate(y_test):if y_pred[i]>=0.7:y_pred[i]=1else:y_pred[i]=0if y == y_pred[i]:true += 1print('Correct Prediction: {}'.format(true))
print('Wrong Prediction: {}'.format(len(y_pred) - true))
print('Accuracy: {}'.format(true/len(y_pred)*100))

测试模型

测试样本测试，输出精度

y_pred = model.predict(x_test, batch_size = 64)
y_pred

y_pred = model.predict(x_test, batch_size = 128)
y_pred=np.argmax(y_pred,axis=-1)
true = 0
for i, y in enumerate(y_test):if y == y_pred[i]:true += 1print('Correct Prediction: {}'.format(true))
print('Wrong Prediction: {}'.format(len(y_pred) - true))
print('Accuracy: {}'.format(true/len(y_pred)*100))

加载已训练好的模型

用已经训练好的深度模型去预测一条新的电影评论的情感

loaded_model = load_model('models/LSTM.h5')

自行输入一条评论（用英文）

review = str(input('Movie Review: '))

预测之前这条新的评论也需要进行预处理

# Pre-process input
regex = re.compile(r'[^a-zA-Z\s]')
review = regex.sub('', review)
print('Cleaned: ', review)words = review.split(' ')
filtered = [w for w in words if w not in english_stops]
filtered = ' '.join(filtered)
filtered = [filtered.lower()]print('Filtered: ', filtered)

对这条新评论进行分词和编码

tokenize_words = token.texts_to_sequences(filtered)
tokenize_words = pad_sequences(tokenize_words, maxlen=max_length, padding='post', truncating='post')
print(tokenize_words)

结果显示了预测的置信度分数 confidence score

result = loaded_model.predict(tokenize_words)
print(result)

若置信度分数接近0则评论为负面 negative. 若置信度分数接近1则评论为正面 positive. 这里选择 0.7 作为置信度阈值，如果分数大于0.7判定为正面，如果分数小于0.7则判定为负面

if result >= 0.7:print('positive')
else:print('negative')