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 __add__(self, other):
      if not isinstance(other, SingleFieldIndexer):
          raise TypeError(
              "Make sure Spark map function return the same indexer type"
          )
      if self._column_name != other._column_name:
          raise ValueError(
              "Make sure indexers in Spark map function index the same fields"
          )
  
      for value_key in other._index_data:
          self._index_data[value_key].update(
              other._index_data[value_key]
          )
  
      return self
  
imports: import numpy
  from collections import defaultdict
  from petastorm.etl import RowGroupIndexerBase
label_desc: Use image node_id 2 for calling the SingleFieldIndexer obj's underlying member method code with example usage: obj.__add__(other) and returns: self