docstr: Group elements by selector, apply fn to each group, and return a list
  of the results.
code: def group_map(self, selector, fn):
      """
      Group elements by selector, apply fn to each group, and return a list
      of the results.
      """
      return self.group(selector).map(fn)
  
imports: import collections
  import inspect
  import json
  import types
  import unittest
  import warnings
  import math
  import numpy
label_desc: Use image node_id 9 for calling the Q obj's underlying member method code with example usage: obj.group_map(selector, fn) and returns: self