【深度学习前沿应用】文本分类Fine-Tunning

前言

应用BERT模型做短文本情绪分类

#导入相关的模块
import paddle
import paddlenlp as ppnlp
from paddlenlp.data import Stack, Pad, Tuple
import paddle.nn.functional as F
import numpy as np
from functools import partial #partial()函数可以用来固定某些参数值，并返回一个新的callable对象
ppnlp.__version__

一、数据加载及预处理

(一)、数据导入

数据集为公开中文情感分析数据集ChnSenticorp。使用PaddleNLP的.datasets.ChnSentiCorp.get_datasets方法即可以加载该数据集。

#采用paddlenlp内置的ChnSentiCorp语料，该语料主要可以用来做情感分类。训练集用来训练模型，验证集用来选择模型，测试集用来评估模型泛化性能。
train_ds, dev_ds, test_ds = ppnlp.datasets.ChnSentiCorp.get_datasets(['train','dev','test'])

#获得标签列表
label_list = train_ds.get_labels()

#看看数据长什么样子，分别打印训练集、验证集、测试集的前3条数据。
print("训练集数据：{}\n".format(train_ds[0:1]))
print("验证集数据:{}\n".format(dev_ds[0:1]))
print("测试集数据:{}\n".format(test_ds[0:1]))

print("训练集样本个数:{}".format(len(train_ds)))
print("验证集样本个数:{}".format(len(dev_ds)))
print("测试集样本个数:{}".format(len(test_ds)))

输出结果如下图1所示：

(二)、数据预处理

#调用ppnlp.transformers.BertTokenizer进行数据处理，tokenizer可以把原始输入文本转化成模型model可接受的输入数据格式。
tokenizer = ppnlp.transformers.BertTokenizer.from_pretrained("bert-base-chinese")

#数据预处理
def convert_example(example,tokenizer,label_list,max_seq_length=256,is_test=False):
    if is_test:
        text = example
    else:
        text, label = example
    #tokenizer.encode方法能够完成切分token，映射token ID以及拼接特殊token
    encoded_inputs = tokenizer.encode(text=text, max_seq_len=max_seq_length)
    # print('===================')
    # print(encoded_inputs)
    input_ids = encoded_inputs["input_ids"]
    segment_ids = encoded_inputs["token_type_ids"]

    if not is_test:
        label_map = {}
        for (i, l) in enumerate(label_list):
            label_map[l] = i

        label = label_map[label]
        label = np.array([label], dtype="int64")
        return input_ids, segment_ids, label
    else:
        return input_ids, segment_ids

#数据迭代器构造方法
def create_dataloader(dataset, trans_fn=None, mode='train', batch_size=1, use_gpu=False, pad_token_id=0, batchify_fn=None):
    if trans_fn:
        dataset = dataset.apply(trans_fn, lazy=True)

    if mode == 'train' and use_gpu:
        sampler = paddle.io.DistributedBatchSampler(dataset=dataset, batch_size=batch_size, shuffle=True)
    else:
        shuffle = True if mode == 'train' else False #如果不是训练集，则不打乱顺序
        sampler = paddle.io.BatchSampler(dataset=dataset, batch_size=batch_size, shuffle=shuffle) #生成一个取样器
    dataloader = paddle.io.DataLoader(dataset, batch_sampler=sampler, return_list=True, collate_fn=batchify_fn)
    return dataloader

#使用partial()来固定convert_example函数的tokenizer, label_list, max_seq_length, is_test等参数值
trans_fn = partial(convert_example, tokenizer=tokenizer, label_list=label_list, max_seq_length=128, is_test=False)
batchify_fn = lambda samples, fn=Tuple(Pad(axis=0,pad_val=tokenizer.pad_token_id), Pad(axis=0, pad_val=tokenizer.pad_token_id), Stack(dtype="int64")):[data for data in fn(samples)]
#训练集迭代器
train_loader = create_dataloader(train_ds, mode='train', batch_size=64, batchify_fn=batchify_fn, trans_fn=trans_fn)
#验证集迭代器

dev_loader = create_dataloader(dev_ds, mode='dev', batch_size=64, batchify_fn=batchify_fn, trans_fn=trans_fn)
#测试集迭代器
test_loader = create_dataloader(test_ds, mode='test', batch_size=64, batchify_fn=batchify_fn, trans_fn=trans_fn)

二、BERT预训练模型加载

#加载预训练模型Bert用于文本分类任务的Fine-tune网络BertForSequenceClassification, 它在BERT模型后接了一个全连接层进行分类。
#由于本任务中的情感分类是二分类问题，设定num_classes为2
model = ppnlp.transformers.BertForSequenceClassification.from_pretrained("bert-base-chinese", num_classes=2)

三、训练模型

(一)、设置训练超参数

#设置训练超参数

#学习率
learning_rate = 1e-5 
#训练轮次
epochs = 8
#学习率预热比率
warmup_proption = 0.1
#权重衰减系数
weight_decay = 0.01

num_training_steps = len(train_loader) * epochs
num_warmup_steps = int(warmup_proption * num_training_steps)

def get_lr_factor(current_step):
    if current_step < num_warmup_steps:
        return float(current_step) / float(max(1, num_warmup_steps))
    else:
        return max(0.0,
                    float(num_training_steps - current_step) /
                    float(max(1, num_training_steps - num_warmup_steps)))
#学习率调度器
lr_scheduler = paddle.optimizer.lr.LambdaDecay(learning_rate, lr_lambda=lambda current_step: get_lr_factor(current_step))

#优化器
optimizer = paddle.optimizer.AdamW(
    learning_rate=lr_scheduler,
    parameters=model.parameters(),
    weight_decay=weight_decay,
    apply_decay_param_fun=lambda x: x in [
        p.name for n, p in model.named_parameters()
        if not any(nd in n for nd in ["bias", "norm"])
    ])

#损失函数
criterion = paddle.nn.loss.CrossEntropyLoss()
#评估函数
metric = paddle.metric.Accuracy()

(二)、评估函数

#评估函数
def evaluate(model, criterion, metric, data_loader):
    model.eval()
    metric.reset()
    losses = []
    for batch in data_loader:
        input_ids, segment_ids, labels = batch
        logits = model(input_ids, segment_ids)
        loss = criterion(logits, labels)
        losses.append(loss.numpy())
        correct = metric.compute(logits, labels)
        metric.update(correct)
        accu = metric.accumulate()
    print("eval loss: %.5f, accu: %.5f" % (np.mean(losses), accu))
    model.train()
    metric.reset()

(三)、模型训练

#开始训练
global_step = 0
for epoch in range(1, epochs + 1):
    for step, batch in enumerate(train_loader): #从训练数据迭代器中取数据
        # print(batch)
        input_ids, segment_ids, labels = batch
        logits = model(input_ids, segment_ids)
        loss = criterion(logits, labels) #计算损失
        probs = F.softmax(logits, axis=1)
        correct = metric.compute(probs, labels)
        metric.update(correct)
        acc = metric.accumulate()

        global_step += 1
        if global_step % 50 == 0 :
            print("global step %d, epoch: %d, batch: %d, loss: %.5f, acc: %.5f" % (global_step, epoch, step, loss, acc))
        loss.backward()
        optimizer.step()
        lr_scheduler.step()
        optimizer.clear_gradients()
    evaluate(model, criterion, metric, dev_loader)

四、模型预测

def predict(model, data, tokenizer, label_map, batch_size=1):
    examples = []
    for text in data:
        input_ids, segment_ids = convert_example(text, tokenizer, label_list=label_map.values(),  max_seq_length=128, is_test=True)
        examples.append((input_ids, segment_ids))

    batchify_fn = lambda samples, fn=Tuple(Pad(axis=0, pad_val=tokenizer.pad_token_id), Pad(axis=0, pad_val=tokenizer.pad_token_id)): fn(samples)
    batches = []
    one_batch = []
    for example in examples:
        one_batch.append(example)
        if len(one_batch) == batch_size:
            batches.append(one_batch)
            one_batch = []
    if one_batch:
        batches.append(one_batch)

    results = []
    model.eval()
    for batch in batches:
        input_ids, segment_ids = batchify_fn(batch)
        input_ids = paddle.to_tensor(input_ids)
        segment_ids = paddle.to_tensor(segment_ids)
        logits = model(input_ids, segment_ids)
        probs = F.softmax(logits, axis=1)
        idx = paddle.argmax(probs, axis=1).numpy()
        idx = idx.tolist()
        labels = [label_map[i] for i in idx]
        results.extend(labels)
    return results

data = ['这个商品虽然看着样式挺好看的，但是不耐用。', '这个老师讲课水平挺高的。']
label_map = {0: '负向情绪', 1: '正向情绪'}

predictions = predict(model, data, tokenizer, label_map, batch_size=32)
for idx, text in enumerate(data):
    print('预测文本: {} \n情绪标签: {}'.format(text, predictions[idx]))

输出结果如下图2所示：

总结

本系列文章内容为根据清华社出版的《机器学习实践》所作的相关笔记和感悟，其中代码均为基于百度飞桨开发，若有任何侵权和不妥之处，请私信于我，定积极配合处理，看到必回！！！

最后，引用本次活动的一句话，来作为文章的结语～(￣▽￣～)~：

【学习的最大理由是想摆脱平庸，早一天就多一份人生的精彩；迟一天就多一天平庸的困扰。】