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 map_transform(self, data: DataEntry, is_train: bool) -> DataEntry:
      if self.allow_missing:
          return {f: data[f] for f in self.input_fields if f in data}
      return {f: data[f] for f in self.input_fields}
  
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 2 for calling the SelectFields obj's underlying member method code with example usage: obj.map_transform(data, is_train) and returns: unknown, unknown