class_docstr: Generate data with matching histogram.
  
  :param embedding_matrix: The embedding matrix used to generator match
                           histogram.
  :param bin_size: The number of bin size of the histogram.
  :param hist_mode: The mode of the :class:`MatchingHistogramUnit`, one of
                   `CH`, `NH`, and `LCH`.
docstr: Insert `match_histogram` to `x`.
code: def on_batch_unpacked(self, x, y):
      """Insert `match_histogram` to `x`."""
      x["match_histogram"] = _build_match_histogram(
          x, self._match_hist_unit
      )
  
file_path: MatchZoo/matchzoo/data_generator/callbacks/histogram.py
imports: import numpy
  import matchzoo
  from matchzoo.data_generator.callbacks import Callback
label_desc: Use image node_id 2 for calling the Histogram obj's underlying member method code with example usage: obj.on_batch_unpacked(x, y) without return types