# Odd dataset.map() behavior with PyTorch dataloader
**URL:**
**Author:**  [@irow](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Fu%2Firow)%5C
**Post date:** [March 25, 2024, 10:06pm UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fodd-dataset-map-behavior-with-pytorch-dataloader%2F78692%2F1 "2024-03-25T22:06:54Z")
Hi all, I’m using a streaming dataset, and then passing that into a normal PyTorch DataLoader. I have a simple map function that pads various sequences in the dataset.
```auto
def pad_map(x):
x['words1'] = pad(x['words1'])
x['words2'] = pad(x['words2'])
x['tags1'] = pad(x['tags1'])
x['tags2'] = pad(x['tags2'])
return x
```
when I pass the dataset into the PyTorch DataLoader (for example with a batch\_size of 4), I get this unexpected result.
```auto
batch = {'words1': [tensor([44, 3399, 419, 3256]),
tensor([312, 222, 667, 290]),
tensor([120, 883, 99, 101]),
...
tensor([0, 0, 0, 0]),
tensor([0, 0, 0, 0]),
tensor([0, 0, 0, 0]),
tensor([0, 0, 0, 0])],
'label': tensor([1, 0, 0, 0])}
```
The only way I see to fix this is to do `torch.stack(batch['words1']).T` to get the proper format.
Is there any way for the map function to produce an output that like the following ?
`{'words1': tensor of shape (batch_size, seq_len), ..., 'labels': tensor of shape (batch_size, )}`
Thanks for your help!
---
**Author:**  [@irow](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Fu%2Firow)%5C
**Post date:** [March 25, 2024, 11:09pm UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fodd-dataset-map-behavior-with-pytorch-dataloader%2F78692%2F2 "2024-03-25T23:09:54Z")
I figured it out, creating a tensor in the map function stopped it from batching it strangely. So like
```auto
def pad_map(x):
x['words1'] = torch.tensor(pad(x['words1']))
x['words2'] = torch.tensor(pad(x['words2']))
x['tags1'] = torch.tensor(pad(x['tags1']))
x['tags2'] = torch.tensor(pad(x['tags2']))
return x
```
---
**Author:**  [@system](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Fu%2Fsystem)%5C
**Post date:** [March 26, 2024, 11:09am UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fodd-dataset-map-behavior-with-pytorch-dataloader%2F78692%2F3 "2024-03-26T11:09:59Z")
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