equal operation to perform unbatch for huggingface datasets 
Hi
I need to use "unbatch" operation in tensorflow on a huggingface dataset, I could not find this operation, could you kindly direct me how I can do it, here is the problem I am trying to solve:

I am considering "record" dataset in SuperGlue and I need to replicate each entery of the dataset for each answer, to make it similar to what T5 originally did:

https://github.com/google-research/text-to-text-transfer-transformer/blob/3c58859b8fe72c2dbca6a43bc775aa510ba7e706/t5/data/preprocessors.py#L925

Here please find an example:

  For example, a typical example from ReCoRD might look like
  {
      'passsage': 'This is the passage.',
      'query': 'A @placeholder is a bird.',
      'entities': ['penguin', 'potato', 'pigeon'],
      'answers': ['penguin', 'pigeon'],
  }
  and I need a prosessor which would turn this example into the following two examples:
  {
      'inputs': 'record query: A @placeholder is a bird. entities: penguin, '
                'potato, pigeon passage: This is the passage.',
      'targets': 'penguin',
  }
  and
  {
      'inputs': 'record query: A @placeholder is a bird. entities: penguin, '
                'potato, pigeon passage: This is the passage.',
      'targets': 'pigeon',
  }


For doing this, one need unbatch, as each entry can map to multiple samples depending on the number of answers, I am not sure how to perform this operation with  huggingface datasets library and greatly appreciate your help

@lhoestq 

Thank you very much.
