code: def batchstack(size, iterable=None, rest=False):
      
  
      def stack(data):
          import numpy as np
          return map(np.vstack, data)
  
      fn = batchzip(size, rest=rest) >> flow(stack)
  
      return fn if iterable is None else fn(iterable)
docs: todo : add example
      :param size:
      :param iterable:
      :param rest:
      :return: