old_contents: from chainer.dataset import dataset_mixin
  
  
  class TransformDataset(dataset_mixin.DatasetMixin):
  
      """Dataset that indexes the base dataset and transforms the data.
  
      This dataset wraps the base dataset by modifying the behavior of the base
      dataset's :meth:`__getitem__`. Arrays returned by :meth:`__getitem__` of
      the base dataset with integer as an argument are transformed by the given
      function :obj:`transform`.
  
      The function :obj:`transform` takes, as an argument, :obj:`in_data`, which
      is the output of the base dataset's :meth:`__getitem__`, and returns
      the transformed arrays as output. Please see the following example.
  
      >>> from chainer.datasets import get_mnist
      >>> from chainer.datasets import TransformDataset
      >>> dataset, _ = get_mnist()
      >>> def transform(in_data):
      >>>     img, label = in_data
      >>>     img -= 0.5  # scale to [-0.5, -0.5]
      >>>     return img, label
      >>> dataset = TransformDataset(dataset, transform)
  
      Args:
          dataset: The underlying dataset. The index of this dataset corresponds
              to the index of the base dataset.
          transform (callable): A function that is called to transform values
              returned by the underlying dataset's :meth:`__getitem__`.
  
      """
  
      def __init__(self, dataset, transform):
          self._dataset = dataset
          self._transform = transform
  
      def get_example(self, i):
          in_data = self._dataset[i]
          return self._transform(in_data)
  
      def __len__(self):
          return len(self._dataset)
  
new_contents: from chainer.dataset import dataset_mixin
  
  
  class TransformDataset(dataset_mixin.DatasetMixin):
  
      """Dataset that indexes the base dataset and transforms the data.
  
      This dataset wraps the base dataset by modifying the behavior of the base
      dataset's :meth:`__getitem__`. Arrays returned by :meth:`__getitem__` of
      the base dataset with integer as an argument are transformed by the given
      function :obj:`transform`.
  
      The function :obj:`transform` takes, as an argument, :obj:`in_data`, which
      is the output of the base dataset's :meth:`__getitem__`, and returns
      the transformed arrays as output. Please see the following example.
  
      >>> from chainer.datasets import get_mnist
      >>> from chainer.datasets import TransformDataset
      >>> dataset, _ = get_mnist()
      >>> def transform(in_data):
      ...     img, label = in_data
      ...     img -= 0.5  # scale to [-0.5, -0.5]
      ...     return img, label
      >>> dataset = TransformDataset(dataset, transform)
  
      Args:
          dataset: The underlying dataset. The index of this dataset corresponds
              to the index of the base dataset.
          transform (callable): A function that is called to transform values
              returned by the underlying dataset's :meth:`__getitem__`.
  
      """
  
      def __init__(self, dataset, transform):
          self._dataset = dataset
          self._transform = transform
  
      def get_example(self, i):
          in_data = self._dataset[i]
          return self._transform(in_data)
  
      def __len__(self):
          return len(self._dataset)
  
subject: change function in document