class_docstr: Groups an Element pair such that we have (ElementX, List[ElementY]).
code: def __init__(self) -> None:  # noqa: D
      self._groups: Dict[
          ElementX, List[ElementY]
      ] = collections.defaultdict(list)
  
file_path: metricflow/metricflow/model/semantics/element_group.py
imports: from __future__ import annotations
  import collections
  from typing import Dict, Generic, List, TypeVar
label_desc: Use image node_id 1 to create a new ElementGrouper object from inherited base classes: Generic with example: obj = ElementGrouper()