docstr: Subtract the histogram splits values on the given key.
  
  Args:
      from_key: the start key
      to_key: the end key
docstr_tok: ["Subtract","the","histogram","splits","values","on","the","given","key",".","Args",":","from_key",":","the","start","key","to_key",":","the","end","key"]
code: def i_sub_on_key(self, from_key: str, to_key: str):
      """
      Subtract the histogram splits values on the given key.
  
      Args:
          from_key: the start key
          to_key: the end key
      """
      self._splits = self._splits.mapValues(
          lambda split: split.i_sub_on_key(from_key, to_key)
      )
  
imports: import logging
  import typing
  from typing import List, MutableMapping, Tuple, Optional
  import torch
  from fate.arch.computing.api import KVTable
  from ._histogram_local import Histogram
  from ._histogram_splits import HistogramSplits
  from .indexer import HistogramIndexer, Shuffler
label_desc: Use image node_id 8 for calling the DistributedHistogram obj's underlying member method code with example usage: obj.i_sub_on_key(from_key, to_key) without return types