class_docstr: Computes NDCG (normalized discounted cumulative gain).
class_docstr_tok: ["Computes","NDCG","(","normalized","discounted","cumulative","gain",")","."]
code: def create_accumulator(self):
      return _NDCGAccumulator(len(self._metric_keys))
  
imports: from typing import Dict, Iterable, List, Optional, Tuple, Union
  import apache_beam
  import numpy
  from tensorflow_model_analysis.metrics import metric_types
  from tensorflow_model_analysis.metrics import metric_util
  from tensorflow_model_analysis.proto import config_pb2
  from tensorflow_model_analysis.utils import util
label_desc: Use image node_id 6 for calling the _NDCGCombiner obj's underlying member method code with example usage: obj.create_accumulator() and returns: _NDCGAccumulator