【pytorch】dataset类的使用

一、dataset定义

在PyTorch中，Dataset是数据加载的核心抽象类，其使用流程主要分为自定义数据集和数据加载器配置两部分。
方法的说明：
meth:__getitem__根据索引返回单个样本及其标签。
meth:__len__返回数据集样本总数。

class Dataset(Generic[T_co]):
    r"""An abstract class representing a :class:`Dataset`.

    All datasets that represent a map from keys to data samples should subclass
    it. All subclasses should overwrite :meth:`__getitem__`, supporting fetching a
    data sample for a given key. Subclasses could also optionally overwrite
    :meth:`__len__`, which is expected to return the size of the dataset by many
    :class:`~torch.utils.data.Sampler` implementations and the default options
    of :class:`~torch.utils.data.DataLoader`.

    .. note::
      :class:`~torch.utils.data.DataLoader` by default constructs a index
      sampler that yields integral indices.  To make it work with a map-style
      dataset with non-integral indices/keys, a custom sampler must be provided.
    """

二、dataset类读取数据

from torch.utils.data import Dataset
from PIL import Image
import os


class MyDataset(Dataset):
    def __init__(self, root_dir, label_dir):
        self.root_dir = root_dir
        self.label_dir = label_dir
        self.path = os.path.join(self.root_dir, self.label_dir)
        self.img_path = os.listdir(self.path)

    def __getitem__(self, idx):
        img_name = self.img_path[idx]
        img_item_path = os.path.join(self.root_dir, self.label_dir, img_name)
        img = Image.open(img_item_path)
        label = self.label_dir
        return img, label

    def __len__(self):
        return len(self.img_path)


ants_dataset = MyDataset(root_dir=r'dataset/train', label_dir='ants')

bees_dataset = MyDataset(root_dir=r'dataset/train', label_dir='bees')

train_data = ants_dataset + bees_dataset
print(len(train_data))
print(train_data[0])

输出