datasets freezes 
Pytorch is unable to convert strings to tensors unfortunately.
You can use `set_format(type="torch")` on columns that can be converted to tensors, such as token ids.

This makes me think that we should probably raise an error or at least a warning when one tries to create pytorch tensors out of text columns
Hi, I want to load these two datasets and convert them to Dataset format in torch and the code freezes for me, could you have a look please? thanks 

dataset1 = load_dataset("squad", split="train[:10]")
dataset1 = dataset1.set_format(type='torch', columns=['context', 'answers', 'question'])

dataset2 = load_dataset("imdb", split="train[:10]")
dataset2 = dataset2.set_format(type="torch", columns=["text", "label"])
print(len(dataset1))
