Inconsistent behaviour for DataLoader torch '1.9.0'

vision
1

Hi everyone, I have an issue with the behaviour of the torch.utils.data.DataLoader for a minimal custom torch.utils.data.Dataset.

Here is the dataset

class MyData(Dataset):
  'Characterizes a dataset for PyTorch'
  def __init__(self, data, targets):
        """"Initialization, here display serves to show an example
        if false, it means that we intend to feed the data to a model"""
        self.targets = targets
        self.data = data

  def __len__(self):
        'Denotes the total number of samples'
        return len(self.targets)
    
  def __getitem__(self, index):
        'Generates one sample of data'
        # Select sample
        X = self.data[index]      
        # Load data and get label
        y = self.targets[index]      
        return X,y

But now, if I try to use it within a DataLoader, it doesn’t switch the number of channel to the second dimension of the tensor

Here is a minimal exemple:

train_data = datasets.CIFAR10('../data/cifar', train=True, transform=transforms.ToTensor(), download=False)
test_data = datasets.CIFAR10('../data/cifar', train=False, transform=transforms.ToTensor(), download=False)

source_data = MyData(train_data.data, train_data.targets)
source_loader = torch.utils.data.DataLoader(source_data, batch_size=1024)
c,d = next(iter(source_loader))
c.shape

It it will return shape

torch.Size([1024, 32, 32, 3])

Whereas, if I do it directly the cifar10 dataset. For instance

train_loader = DataLoader(train_data, batch_size=1024, shuffle=True)
a,b = next(iter(train_loader))
a.shape

will return

torch.Size([1024, 3, 32, 32])

I am using

  • torch ‘1.9.0’
  • torchvision ‘0.10.0’
2

Probably you are not applying transform sequence as torchvision’s CIFAR10 does.
Remember that only the raw data is passed as input to your newly written MyData class. All the other post-computations (such as Normalization) should be handled in MyData.