def METHOD_NAME(self, index: int):
    """
    Return an example's size as a float or tuple. Here we return the max
    across all underlying datasets. This value is used when filtering a
    dataset with max-positions.
    """
    return max(
        dataset.METHOD_NAME(self._map_index_to_dataset(key, index))
        for key, dataset in self.datasets.items()
    )