code: def test_multi_group_projection():
      """test grouping by three attributes"""
  
      class _EventInterface(ABC):
          @define_stats_grouping("group1", "group2", "group3")
          @define_step_stats(sum, group_by="group1", output_name="g1")
          @define_step_stats(sum, group_by="group2", output_name="g2")
          @define_step_stats(sum, group_by="group3", output_name="g3")
          def event1(self, group1, group2, group3, attr1):
              pass
  
      agg = LogStatsAggregator(LogStatsLevel.STEP)
      agg.add_event(
          EventRecord(
              _EventInterface,
              _EventInterface.event1,
              dict(group1=1, group2=0, group3=0, attr1=1),
          )
      )
      agg.add_event(
          EventRecord(
              _EventInterface,
              _EventInterface.event1,
              dict(group1=0, group2=1, group3=0, attr1=2),
          )
      )
      agg.add_event(
          EventRecord(
              _EventInterface,
              _EventInterface.event1,
              dict(group1=0, group2=0, group3=1, attr1=4),
          )
      )
  
      stats = agg.reduce()
      assert len(stats) == 6
  
      assert stats[(_EventInterface.event1, "g1", (0, None, None))] == 6
      assert stats[(_EventInterface.event1, "g1", (1, None, None))] == 1
      assert stats[(_EventInterface.event1, "g2", (None, 0, None))] == 5
      assert stats[(_EventInterface.event1, "g2", (None, 1, None))] == 2
      assert stats[(_EventInterface.event1, "g3", (None, None, 0))] == 3
      assert stats[(_EventInterface.event1, "g3", (None, None, 1))] == 4
  
file_path: maze/maze/test/core/test_log_stats.py
imports: from abc import ABC
  import numpy
  import pytest
  from maze.core.events.event_record import EventRecord
  from maze.core.log_stats.event_decorators import define_step_stats, define_episode_stats, define_epoch_stats, define_stats_grouping
  from maze.core.log_stats.log_stats import LogStatsAggregator, LogStatsLevel
  from maze.core.log_stats.reducer_functions import histogram
label_desc: Use image node_id 10 for calling a global function with example usage: test_multi_group_projection() without return types