class_docstr: A mini-batch transformer used to manipulate mini-batch.
  
  Functional name: :obj:`transform`.
  
  Parameters
  ----------
  datapipe : DataPipe
      The datapipe.
  transformer:
      The function applied to each minibatch which is responsible for
      transforming the minibatch.
code: def _transformer(self, minibatch):
      minibatch = self.transformer(minibatch)
      assert isinstance(
          minibatch, (MiniBatch,)
      ), "The transformer output should be an instance of MiniBatch"
      return minibatch
  
imports: from torch.utils.data import functional_datapipe
  from torchdata.datapipes.iter import Mapper
  from .minibatch import MiniBatch
label_desc: Use image node_id 2 for calling the MiniBatchTransformer obj's underlying member method code with example usage: obj._transformer(minibatch) and returns: minibatch