class_docstr: Only keep the listed fields.
  
  Parameters
  ----------
  input_fields
      List of fields to keep.
  allow_missing
      If ``True``, skip any missing field. Default: ``False``.
code: def __init__(
      self, input_fields: List[str], allow_missing: bool = False
  ) -> None:
      self.input_fields = input_fields
      self.allow_missing = allow_missing
  
imports: from collections import Counter
  from typing import Any, Dict, List
  from gluonts.core.component import validated
  from gluonts.dataset.common import DataEntry
  from ._base import MapTransformation, SimpleTransformation
label_desc: Use image node_id 1 to create a new SelectFields object from inherited base classes: MapTransformation with example: obj = SelectFields(input_fields, allow_missing)