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 column_names(self):
      return [self._column_name]
  
imports: import numpy
  from collections import defaultdict
  from petastorm.etl import RowGroupIndexerBase
label_desc: Use image node_id 4 for calling the SingleFieldIndexer obj's underlying member method code with example usage: obj.column_names() and returns: list