背景:

    基于手机的20列特征 -> 预测手机的价格区间(4个区间), 可以用机器学习做, 也可以用 深度学习做(推荐)

 

ANN案例的实现步骤:

    1. 构建数据集.

    2. 搭建神经网络.

    3. 模型训练.

    4. 模型测试.

import torch
import torch.nn as nn
import pandas as pd
from sklearn.model_selection import train_test_split
from torch.utils.data import TensorDataset
from torch.utils.data import DataLoader
import torch.optim as optim
import numpy as np
import time
from sklearn.preprocessing import StandardScaler


# 构建数据集
def create_dataset():
	# 使用pandas读取数据
	data = pd.read_csv('./data/手机价格预测.csv')
	# 特征值和目标值
	x, y = data.iloc[:, :-1], data.iloc[:, -1]
	# 类型转换：特征值，目标值
	x = x.astype(np.float32)
	y = y.astype(np.int64)
	# 数据集划分
	x_train, x_valid, y_train, y_valid = train_test_split(x, y, train_size=0.8, random_state=88, stratify=y)
	# 优化①:数据标准化
	transfer = StandardScaler()
	x_train = transfer.fit_transform(x_train)
	x_valid = transfer.transform(x_valid)
	# 构建数据集,转换为pytorch的形式
	train_dataset = TensorDataset(torch.from_numpy(x_train), torch.tensor(y_train.values))
	valid_dataset = TensorDataset(torch.from_numpy(x_valid), torch.tensor(y_valid.values))
	# 返回结果
	return train_dataset, valid_dataset, x_train.shape[1], len(np.unique(y))


# 构建网络模型
class PhonePriceModel(nn.Module):

	def __init__(self, input_dim, output_dim):
		super(PhonePriceModel, self).__init__()
		# 优化②:增加网络深度
		# 1. 第一层: 输入为维度为 20, 输出维度为: 128
		self.linear1 = nn.Linear(input_dim, 128)
		# 2. 第二层: 输入为维度为 128, 输出维度为: 256
		self.linear2 = nn.Linear(128, 256)
		# 3. 第三层: 输入为维度为 256, 输出维度为: 512
		self.linear3 = nn.Linear(256, 512)
		# 4. 第四层: 输入为维度为 512, 输出维度为: 128
		self.linear4 = nn.Linear(512, 128)
		# 5. 输出层: 输入为维度为 128, 输出维度为: 4
		self.linear5 = nn.Linear(128, output_dim)

	def forward(self, x):
		# 前向传播过程
		x = torch.relu(self.linear1(x))
		x = torch.relu(self.linear2(x))
		x = torch.relu(self.linear3(x))
		x = torch.relu(self.linear4(x))
		# 后续CrossEntropyLoss损失函数中包含softmax过程, 所以当前步骤不进行softmax操作
		output = self.linear5(x)
		# 获取数据结果
		return output


# 编写训练函数
def train(train_dataset, input_dim, class_num):
	# 固定随机数种子
	torch.manual_seed(0)
	# 初始化数据加载器
	dataloader = DataLoader(train_dataset, shuffle=True, batch_size=8)
	# 初始化模型
	model = PhonePriceModel(input_dim, class_num)
	# 损失函数 CrossEntropyLoss = softmax + 损失计算
	criterion = nn.CrossEntropyLoss()
	# 优化③:使用Adam优化方法, 优化④:学习率变为1e-4
	optimizer = optim.Adam(model.parameters(), lr=1e-4)
	# 遍历每个轮次的数据
	num_epoch = 50
	for epoch_idx in range(num_epoch):
		# 训练时间
		start = time.time()
		# 计算损失
		total_loss = 0.0
		total_num = 0
		# 遍历每个batch数据进行处理
		for x, y in dataloader:
			model.train()
			output = model(x)
			# 计算损失
			loss = criterion(output, y)
			# 梯度清零
			optimizer.zero_grad()
			# 反向传播
			loss.backward()
			# 参数更新
			optimizer.step()
			# 损失计算
			total_num += len(y)
			total_loss += loss.item() * len(y)
		# 打印损失变换结果
		print('epoch: %4s loss: %.2f, time: %.2fs' %
			  (epoch_idx + 1, total_loss / total_num, time.time() - start))
	# 模型保存
	torch.save(model.state_dict(), './model/phone-price-model2.pth')


def evaluate(valid_dataset, input_dim, class_num):
	# 加载模型和训练好的网络参数
	model = PhonePriceModel(input_dim, class_num)
	# load_state_dict:将加载的参数字典应用到模型上
	# load:加载用来保存模型参数的文件
	model.load_state_dict(torch.load('./model/phone-price-model2.pth'))
	# 构建加载器
	dataloader = DataLoader(valid_dataset, batch_size=8, shuffle=False)
	# 评估测试集
	correct = 0
	# 遍历测试集中的数据
	for x, y in dataloader:
		# 将其送入网络中
		# model.eval()
		output = model(x)
		# 获取预测类别结果
		y_pred = torch.argmax(output, dim=1)
		# 获取预测正确的个数
		correct += (y_pred == y).sum()
	# 求预测精度
	print('Acc: %.5f' % (correct / len(valid_dataset)))


if __name__ == '__main__':
	train_dataset, valid_dataset, input_dim, class_num = create_dataset()
	train(train_dataset, input_dim, class_num)
	evaluate(valid_dataset, input_dim, class_num)