PyTorch翻译官网教程4-TRANSFORMS

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Transforms — PyTorch Tutorials 2.0.1+cu117 documentation

TRANSFORMS

数据并不总是以训练机器学习算法所需的最终处理形式出现,我们使用transforms对数据进行一些操作，使其适合于训练。

所有的TorchVision数据集都有两个参数，transform用于修改特征，target_transform用于修改标签。这两个参数为调用函数，包含转换逻辑。 torchvision.transforms 模块提供了几种常用的开箱即用的transform。

FashionMNIST的特征为PIL Image格式，标签为integer格式。为了训练，我们需要将特征转换为归一化处理的张量，将标签转换为one-hot编码的张量。为了完成这些转换，我们使用ToTensor和Lambda。

import torch
from torchvision import datasets
from torchvision.transforms import ToTensor, Lambda

ds = datasets.FashionMNIST(
    root="data",
    train=True,
    download=True,
    transform=ToTensor(),
    target_transform=Lambda(lambda y: torch.zeros(10, dtype=torch.float).scatter_(0, torch.tensor(y), value=1))
)

输出

Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/train-images-idx3-ubyte.gz
Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/train-images-idx3-ubyte.gz to data/FashionMNIST/raw/train-images-idx3-ubyte.gz

  0%|          | 0/26421880 [00:00<?, ?it/s]
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  3%|2         | 720896/26421880 [00:00<00:12, 2002640.95it/s]
  6%|5         | 1540096/26421880 [00:00<00:07, 3218256.61it/s]
 16%|#5        | 4227072/26421880 [00:00<00:02, 9447718.64it/s]
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 70%|######9   | 18448384/26421880 [00:01<00:00, 17609718.89it/s]
 79%|#######9  | 20905984/26421880 [00:01<00:00, 16403516.46it/s]
 88%|########8 | 23298048/26421880 [00:01<00:00, 18134303.49it/s]
 98%|#########7| 25886720/26421880 [00:01<00:00, 17102426.93it/s]
100%|##########| 26421880/26421880 [00:02<00:00, 13182141.90it/s]
Extracting data/FashionMNIST/raw/train-images-idx3-ubyte.gz to data/FashionMNIST/raw

Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/train-labels-idx1-ubyte.gz
Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/train-labels-idx1-ubyte.gz to data/FashionMNIST/raw/train-labels-idx1-ubyte.gz

  0%|          | 0/29515 [00:00<?, ?it/s]
100%|##########| 29515/29515 [00:00<00:00, 327759.82it/s]
Extracting data/FashionMNIST/raw/train-labels-idx1-ubyte.gz to data/FashionMNIST/raw

Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/t10k-images-idx3-ubyte.gz
Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/t10k-images-idx3-ubyte.gz to data/FashionMNIST/raw/t10k-images-idx3-ubyte.gz

  0%|          | 0/4422102 [00:00<?, ?it/s]
  1%|1         | 65536/4422102 [00:00<00:11, 363698.07it/s]
  5%|5         | 229376/4422102 [00:00<00:06, 683312.59it/s]
 14%|#4        | 622592/4422102 [00:00<00:02, 1702377.65it/s]
 36%|###5      | 1572864/4422102 [00:00<00:00, 3401498.22it/s]
 76%|#######5  | 3342336/4422102 [00:00<00:00, 7182283.54it/s]
100%|##########| 4422102/4422102 [00:00<00:00, 5435154.93it/s]
Extracting data/FashionMNIST/raw/t10k-images-idx3-ubyte.gz to data/FashionMNIST/raw

Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/t10k-labels-idx1-ubyte.gz
Downloading http://fashion-mnist.s3-website.eu-central-1.amazonaws.com/t10k-labels-idx1-ubyte.gz to data/FashionMNIST/raw/t10k-labels-idx1-ubyte.gz

  0%|          | 0/5148 [00:00<?, ?it/s]
100%|##########| 5148/5148 [00:00<00:00, 31293155.06it/s]
Extracting data/FashionMNIST/raw/t10k-labels-idx1-ubyte.gz to data/FashionMNIST/raw

ToTensor()

ToTensor将PIL图像或NumPy数组转换为FloatTensor。并在[0,1]范围内缩放图像的像素强度值。

Lambda Transforms

Lambda transforms应用于任何用户定义的Lambda函数。在这里，我们定义一个函数来将整数转换为一个one-hot 编码张量。它首先创建一个大小为10的零张量(我们数据集中的标签数量)，并调用scatter_，它对标签y给出的索引赋值=1。

target_transform = Lambda(lambda y: torch.zeros(
    10, dtype=torch.float).scatter_(dim=0, index=torch.tensor(y), value=1))