class_docstr: Builtin reduce function that aggregates a single field into another
  single field.
class_docstr_tok: ["Builtin","reduce","function","that","aggregates","a","single","field","into","another","single","field","."]
code: def __init__(self, name, msg_field, out_field):
      self._name = name
      self.msg_field = msg_field
      self.out_field = out_field
  
file_path: dgl/python/dgl/function/reducer.py
imports: from __future__ import absolute_import
  import sys
  from .base import BuiltinFunction
label_desc: Use image node_id 1 to create a new SimpleReduceFunction object from inherited base classes: ReduceFunction with example: obj = SimpleReduceFunction(name, msg_field, out_field)