class_docstr: Class to index single field in parquet dataset.
  
  This indexer only indexes numpty strings, numpty integers, or numpy arrays of strings.
class_docstr_tok: ["Class","to","index","single","field","in","parquet","dataset",".","This","indexer","only","indexes","numpty","strings",",","numpty","integers",",","or","numpy","arrays","of","strings","."]
code: def __init__(self, index_name, index_field):
      self._index_name = index_name
      self._column_name = index_field
      self._index_data = defaultdict(set)
  
imports: import numpy
  from collections import defaultdict
  from petastorm.etl import RowGroupIndexerBase
label_desc: Use image node_id 1 to create a new SingleFieldIndexer object from inherited base classes: RowGroupIndexerBase with example: obj = SingleFieldIndexer(index_name, index_field)