class_docstr: Class to index 'Not Null' condition forsingle field in parquet dataset
class_docstr_tok: ["Class","to","index","'Not","Null","'","condition","forsingle","field","in","parquet","dataset"]
code: def __init__(self, index_name, index_field):
      self._index_name = index_name
      self._column_name = index_field
      self._index_data = set()
  
imports: import numpy
  from collections import defaultdict
  from petastorm.etl import RowGroupIndexerBase
label_desc: Use image node_id 1 to create a new FieldNotNullIndexer object from inherited base classes: RowGroupIndexerBase with example: obj = FieldNotNullIndexer(index_name, index_field)