docs: def convert_sparse_to_dataframe(spark, context, sparse_matrix):
      """ Converts a scipy sparse matrix to a spark dataframe """
      m = sparse_matrix.tocoo()
      data = context.parallelize(numpy.array([m.row, m.col, m.data]).T,
                                 numSlices=len(m.row)/1024)
      return spark.createDataFrame(data.map(lambda p: Row(row=int(p[0]),
                                                          col=int(p[1]),
                                                          data=float(p[2]))))