code: def approxNearestNeighbors(self, dataset, key, numNearestNeighbors, distCol="distCol"):
          
          return self._call_java("approxNearestNeighbors", dataset, key, numNearestNeighbors,
                                 distCol)
docs: Given a large dataset and an item, approximately find at most k items which have the
          closest distance to the item. If the :py:attr:`outputCol` is missing, the method will
          transform the data; if the :py:attr:`outputCol` exists, it will use that. This allows
          caching of the transformed data when necessary.
  
          .. note:: This method is experimental and will likely change behavior in the next release.
  
          :param dataset: The dataset to search for nearest neighbors of the key.
          :param key: Feature vector representing the item to search for.
          :param numNearestNeighbors: The maximum number of nearest neighbors.
          :param distCol: Output column for storing the distance between each result row and the key.
                          Use "distCol" as default value if it's not specified.
          :return: A dataset containing at most k items closest to the key. A column "distCol" is
                   added to show the distance between each row and the key.