在Pytorch上具有相同标签的点的批次 [英] Batches of points with the same label on Pytorch
问题描述
我想在每个包含N个训练点的批次上使用梯度下降训练一个神经网络.我希望这些批次仅包含具有相同标签的点,而不是从训练集中随机取样.
I want to train a neural network using gradient descent on batches that contain N training points each. I would like these batches to only contain points with the same label, instead of being randomly sampled from the training set.
例如,如果我正在使用MNIST进行训练,我希望拥有如下所示的批次:
For example, if I'm training using MNIST, I would like to have batches that look like the following:
batch_1 = {0,0,0,0,0,0,0,0}
batch_2 = {3,3,3,3,3,3,3,3}
batch_3 = {7,7,7,7,7,7,7,7}
...
,依此类推.
我该如何使用pytorch?
How can I do it using pytorch?
推荐答案
一种方法是为每个类创建子集和数据加载器,然后在每次迭代时通过在数据加载器之间随机切换来进行迭代:
One way to do it is to create subsets and dataloaders for each class and then iterate by randomly switching between the dataloaders at each iteration:
import torch
from torch.utils.data import DataLoader, Subset
from torchvision.datasets import MNIST
from torchvision import transforms
import numpy as np
dataset = MNIST('path/to/mnist_root/',
transform=transforms.ToTensor(),
download=True)
class_inds = [torch.where(dataset.targets == class_idx)[0]
for class_idx in dataset.class_to_idx.values()]
dataloaders = [
DataLoader(
dataset=Subset(dataset, inds),
batch_size=8,
shuffle=True,
drop_last=False)
for inds in class_inds]
epochs = 1
for epoch in range(epochs):
iterators = list(map(iter, dataloaders))
while iterators:
iterator = np.random.choice(iterators)
try:
images, labels = next(iterator)
print(labels)
# do_more_stuff()
except StopIteration:
iterators.remove(iterator)
这将适用于任何数据集(不仅限于MNIST).这是每次迭代打印标签的结果:
This will work with any dataset (not just the MNIST). Here's the result of printing the labels at each iteration:
tensor([6, 6, 6, 6, 6, 6, 6, 6])
tensor([3, 3, 3, 3, 3, 3, 3, 3])
tensor([0, 0, 0, 0, 0, 0, 0, 0])
tensor([5, 5, 5, 5, 5, 5, 5, 5])
tensor([8, 8, 8, 8, 8, 8, 8, 8])
tensor([0, 0, 0, 0, 0, 0, 0, 0])
...
tensor([1, 1, 1, 1, 1, 1, 1, 1])
tensor([1, 1, 1, 1, 1, 1])
请注意,通过设置 drop_last = False
,到处将存在具有少于 batch_size
个元素的批次.通过将其设置为True,批次将全部相等,但是将删除一些数据点.
Note that by setting drop_last=False
, there will be batches, here and there, with less than batch_size
elements. By setting it to True, the batches will be all of equal size, but some data points will be dropped.
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