class_docstr: Retrieves neighbour indices according to class labels provided in constructor.
  Rows with the same label will be regarded as neighbours.
docstr: Returns the number of rows in the data
docstr_tok: ["Returns","the","number","of","rows","in","the","data"]
code: def __len__(self):
      """Returns the number of rows in the data"""
      return len(self.labels)
  
imports: from collections.abc import Sequence
  import numpy
label_desc: Use image node_id 2 for calling the LabeledNeighbourMap obj's underlying member method code with example usage: obj.__len__() and returns: len