实战 Kaggle 比赛：图像分类 (CIFAR-10) TOP1 0.97900

首先，导入竞赛所需的包和模块。

import collections
import os
import math
import random
import torch
import torchvision
from d2l import torch as d2l
import shutil
import pandas as pd
from torch import nn

了解一些函数功能

text="      Hello World            "
print(text.strip())
print(text.lstrip())
print(text.rstrip())
a=[1,2,3]
b=[4,5,6]
print(dict(zip(a,b)))
print(dict([("a", 1), ("b", 2)]))

Hello World
Hello World
Hello World
{1: 4, 2: 5, 3: 6}
{'a': 1, 'b': 2}

由于数据量大，这里本地就采用小样本继续train

d2l.DATA_HUB['cifar10_tiny'] = (d2l.DATA_URL + 'kaggle_cifar10_tiny.zip',
'2068874e4b9a9f0fb07ebe0ad2b29754449ccacd')

# 如果使用完整的Kaggle竞赛的数据集，设置demo为False
demo = True

if demo:
data_dir = d2l.download_extract('cifar10_tiny')
else:
data_dir = '../data/cifar-10/'
print(data_dir)

查看数据

def read_cvs_labels(filename):
with open(filename, 'r') as f:
lines = f.readlines()[1:]
tokens = [l.rstrip().split(',') for l in lines]
return dict((name,label) for name,label in tokens)
labels=read_cvs_labels(os.path.join(data_dir, 'trainLabels.csv'))
print(len(labels))
print(len(set(labels.values())))

from collections import Counter

test_labels = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple']
counter = Counter(labels.values())
print(counter.most_common()[-1][1])

copy文件，把train数据分成train and valid and trian+valid

def movefile(filename, target_dir):
# 会自动创建对个目录
shutil.mkdirs(target_dir, exist_ok=True)
shutil.move(filename, target_dir)
def copyfile(filename, target_dir):
# """将文件复制到目标目录""
os.makedirs(target_dir, exist_ok=True)
shutil.copy(filename, target_dir)

def reorg_train_valid(data_dir, labels, valid_ratio):
# 训练数据集中样本最少的类别中的样本数
n = collections.Counter(labels.values()).most_common()[-1][1]
# 验证集中每个类别的样本数
n_valid_per_label = max(1, math.floor(n * valid_ratio))
label_count = {}
for train_file in os.listdir(os.path.join(data_dir, 'train')):
# 获取train目录下的每张图片的标签
label = labels[train_file.split('.')[0]]
fname=os.path.join(data_dir, 'train', train_file)
copyfile(fname, os.path.join(data_dir, 'train_valid_test', 'train_valid', label))
if label not in label_count or label_count[label] < n_valid_per_label:
copyfile(fname, os.path.join(data_dir, 'train_valid_test', 'valid', label))
# 统计每个类别的样本数，每次放入新的图片就加一
label_count[label] = label_count.get(label, 0) + 1
else:
copyfile(fname, os.path.join(data_dir, 'train_valid_test',
'train', label))
return n_valid_per_label

划分

def reorg_test(data_dir):
"""在预测期间整理测试集，以方便读取"""
for test_file in os.listdir(os.path.join(data_dir, 'test')):
copyfile(os.path.join(data_dir, 'test', test_file),
os.path.join(data_dir, 'train_valid_test', 'test',
'unknown'))

读取labels and 划分数据

def reorg_cifar10_data(data_dir, valid_ratio):
labels=read_cvs_labels(os.path.join(data_dir, 'trainLabels.csv'))
reorg_train_valid(data_dir,labels,valid_ratio)
reorg_test(data_dir)

batch_size=8 if demo else 32
valid_ratio=0.1
reorg_cifar10_data(data_dir, valid_ratio)

from torchvision.models import vit_b_16, ViT_B_16_Weights
vit_transform=torchvision.models.ViT_B_16_Weights.DEFAULT.transforms()
# get_net()
print(vit_transform)

Data

# 使用Vit_transform进行数据增强，因为使用了vit_transform的预训练模型
train_ds, train_valid_ds = [torchvision.datasets.ImageFolder(
os.path.join(data_dir, 'train_valid_test', folder),
transform=vit_transform) for folder in ['train', 'train_valid']]
# [torchvision.datasets.ImageFolder label按照文件夹名字排好
valid_ds, test_ds = [torchvision.datasets.ImageFolder(
os.path.join(data_dir, 'train_valid_test', folder),
transform=vit_transform) for folder in ['valid', 'test']]

典型的工作流程：

训练阶段：用 train 训练模型，用 valid 验证并调整超参数。

最终训练阶段：用 train_valid（合并后的数据）重新训练模型（此时不再需要验证集，因为超参数已经固定）。

测试阶段：用 test 评估最终模型性能。

DataLoader

train_iter, train_valid_iter = [torch.utils.data.DataLoader(
dataset, batch_size, shuffle=True, drop_last=True)
for dataset in (train_ds, train_valid_ds)]
# drop_last=True means the last incomplete batch will be dropped

valid_iter = torch.utils.data.DataLoader(valid_ds, batch_size, shuffle=False,
drop_last=True)

test_iter = torch.utils.data.DataLoader(test_ds, batch_size, shuffle=False,
drop_last=False)

获取Vit模型

def get_net():
num_classes = 10
# 加载预训练的 ViT
weight=torchvision.models.ViT_B_16_Weights
net=vit_b_16(weights=weight.DEFAULT)
# fine-tuning：替换分类头
num_ftrs=net.heads.head.in_features
net.fc=nn.Linear(num_ftrs,num_classes)
return net
loss=nn.CrossEntropyLoss(reduction='none')
#     默认情况：如果不指定 reduction 或设置为 'mean'，损失会对所有样本的损失值求平均；如果设置为 'sum'，则对所有样本的损失值求和。
# reduction='none'：不进行任何聚合操作，直接返回每个样本的损失值。假设输入是一个 batch 大小为 N 的数据，则输出是一个形状为 (N,) 的张量，每个元素对应一个样本的损失。

x=[1,2,3]
print(isinstance(x,dict))
print(isinstance(x,list))

定义训练一轮的函数

def train_batch_ch13(net, X, y, loss, trainer, devices):
"""使用多个GPU训练一个小批次（定义在第13章）

定义在 :numref:`sec_image_augmentation` 章节"""

# 将输入数据X转移到第一个GPU设备
# 判断X是否属于List
if isinstance(X, list):
# 用于BERT微调等特殊情况（后续章节会介绍）
X = [x.to(devices[0]) for x in X]
else:
X = X.to(devices[0])

# 将标签y转移到第一个GPU设备
y = y.to(devices[0])

# 设置网络为训练模式
net.train()

# 清空优化器的梯度
trainer.zero_grad()

# 前向传播计算预测值
pred = net(X)

# 计算损失
l = loss(pred, y)

# 反向传播计算梯度（使用mean()而不是sum()，避免受批次大小影响）
l.mean().backward()

# 更新模型参数
trainer.step()

# 计算批次总损失（用于后续统计）
train_loss_sum = l.sum()

# 计算批次准确率
train_acc_sum = d2l.accuracy(pred, y)

return train_loss_sum, train_acc_sum

CFG参数配置

# 参数配置Config
best_params = {'weight_decay': 3.1595250466032746e-05,
'learning_rate': 5e-5,# 0.0007394699205144519
'dropout_rate': 0.10845782679503657}

devices, num_epochs, lr, wd = d2l.try_all_gpus(), 30, best_params['learning_rate'], best_params['weight_decay']
lr_period, lr_decay, net = 4, 0.9, get_net()

定义带Warmup的余弦退火函数

import math
import torch
from torch.optim.lr_scheduler import LambdaLR

def cosine_warmup_scheduler(optimizer, warmup_epochs=5, max_epochs=num_epochs, max_lr=best_params['learning_rate']):
def lr_lambda(current_epoch):
if current_epoch < warmup_epochs:
# 线性 warmup
return float(current_epoch + 1) / float(warmup_epochs)
else:
# 余弦退火
progress = (current_epoch - warmup_epochs) / (max_epochs - warmup_epochs)
return 0.5 * (1.0 + math.cos(math.pi * progress))

for param_group in optimizer.param_groups:
param_group['lr'] = max_lr

return LambdaLR(optimizer, lr_lambda)

开始Train

def train(net, train_iter, valid_iter, num_epochs, lr, wd, devices, lr_period,
lr_decay):
# 初始化优化器：使用随机梯度下降（SGD），设置学习率、动量（momentum）和权重衰减（weight_decay）
# trainer = torch.optim.SGD(net.parameters(), lr=lr, momentum=0.9,
#   weight_decay=wd)
trainer=torch.optim.Adam(net.parameters(),lr=lr,weight_decay=wd)
# 学习率调度器：warmup学习率策略和余弦退火学习率策略
scheduler = cosine_warmup_scheduler(trainer)

# 获取训练集的batch数量，并初始化计时器
num_batches, timer = len(train_iter), d2l.Timer()

# 设置动画显示图例（训练损失、训练准确率，如果有验证集则加上验证准确率）
legend = ['train loss', 'train acc']
if valid_iter is not None:
legend.append('valid acc')

# 初始化动画绘制器（用于可视化训练过程）
animator = d2l.Animator(xlabel='epoch', xlim=[1, num_epochs],
legend=legend)

# 使用多GPU并行训练（DataParallel），主设备为devices[0]
net = nn.DataParallel(net, device_ids=devices).to(devices[0])
# 开始训练循环
for epoch in range(num_epochs):
net.train()  # 设置模型为训练模式
metric = d2l.Accumulator(3)  # 初始化累加器（用于累计损失、准确率、样本数）

# 遍历训练集的每个batch
for i, (features, labels) in enumerate(train_iter):
timer.start()  # 开始计时

# 训练一个batch，返回损失和准确率
l, acc = train_batch_ch13(net, features, labels,
loss, trainer, devices)

# 累加当前batch的损失、准确率、样本数
metric.add(l, acc, labels.shape[0])
timer.stop()  # 停止计时

# 每训练完约1/5的batch或最后一个batch时，更新训练曲线
if (i + 1) % (num_batches // 5) == 0 or i == num_batches - 1:
animator.add(epoch + (i + 1) / num_batches,
(metric[0] / metric[2], metric[1] / metric[2],
None))

# 如果有验证集，计算验证集准确率并更新曲线
if valid_iter is not None:
net.eval()  # 设置模型为评估模式
valid_acc = d2l.evaluate_accuracy_gpu(net, valid_iter)
animator.add(epoch + 1, (None, None, valid_acc))

scheduler.step()  # 更新学习率（按lr_period和lr_decay调整）

# 打印训练结果
measures = (f'train loss {metric[0] / metric[2]:.3f}, '
f'train acc {metric[1] / metric[2]:.3f}')
if valid_iter is not None:
measures += f', valid acc {valid_acc:.3f}'

# 打印训练速度（样本数/秒）和使用的设备
print(measures + f'\n{metric[2] * num_epochs / timer.sum():.1f}'
f' examples/sec on {str(devices)}')

if demo:
# 设置demo为True时进行小批量运行来获取最合适的超参数
train(net, train_iter, valid_iter, num_epochs, lr, wd, devices, lr_period,
lr_decay)
# 0.547 valid acc
else:
net, preds = get_net(), []
net.eval()
train(net, train_valid_iter, None, num_epochs, lr, wd, devices, lr_period,
lr_decay)

for X, _ in test_iter:
y_hat = net(X.to(devices[0]))
preds.extend(y_hat.argmax(dim=1).type(torch.int32).cpu().numpy())
sorted_ids = list(range(1, len(test_ds) + 1))
sorted_ids.sort(key=lambda x: str(x))
df = pd.DataFrame({'id': sorted_ids, 'label': preds})
df['label'] = df['label'].apply(lambda x: train_valid_ds.classes[x])
df.to_csv('submission.csv', index=False)