Pytorch tensor, how to switch channel position - Runtime error

Question

I have my training dataset as below, where X_train is 3D with 3 channels

Shape of X_Train: (708, 256, 3) Shape of Y_Train: (708, 4)

Then I convert them into a tensor and input into the dataloader:

X_train=torch.from_numpy(X_data)
y_train=torch.from_numpy(y_data)
training_dataset = torch.utils.data.TensorDataset(X_train, y_train)
train_loader = torch.utils.data.DataLoader(training_dataset, batch_size=50, shuffle=False)

However when training the model, I get the following error: RuntimeError: Given groups=1, weight of size 24 3 5, expected input[708, 256, 3] to have 3 channels, but got 256 channels instead

I suppose this is due to the position of the channel? In Tensorflow, the channel position is at the end, but in PyTorch the format is "Batch Size x Channel x Height x Width"? So how do I swap the positions in the x_train tensor to match the expected format in the dataloader?

class TwoLayerNet(torch.nn.Module):
    def __init__(self):
        super(TwoLayerNet,self).__init__()
        self.conv1 = nn.Sequential(
            nn.Conv1d(3, 3*8, kernel_size=5, stride=1),  
            nn.Sigmoid(),
            nn.AvgPool1d(kernel_size=2, stride=0))
        self.conv2 = nn.Sequential(
            nn.Conv1d(3*8, 12, kernel_size=5, stride=1),
            nn.Sigmoid(),
            nn.AvgPool1d(kernel_size=2, stride = 0))
        #self.drop_out = nn.Dropout()

        self.fc1 = nn.Linear(708, 732) 
        self.fc2 = nn.Linear(732, 4)

    def forward(self, x):
        out = self.conv1(x)
        out = self.conv2(out)
        out = out.reshape(out.size(0), -1)
        out = self.drop_out(out)
        out = self.fc1(out)
        out = self.fc2(out)
        return out

Does this answer your question? No N-dimensional tranpose in PyTorch — iacob

Coolness Coolness · Accepted Answer · 2020-01-08T14:56:39

Use permute.

X_train = torch.rand(708, 256, 3)
X_train = X_train.permute(2, 0, 1)
X_train.shape
# => torch.Size([3, 708, 256])

Pytorch tensor, how to switch channel position - Runtime error

1 Answers