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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_river_index(self, river_id):
 """ This method retrieves the river index in the netCDF dataset corresponding to the river ID. Parameters river_id: int The ID of the river segment. Returns ------- int: The index of the river ID's in the file. Example:: from RAPIDpy import RAPIDDataset path_to_rapid_qout = '/path/to/Qout.nc' river_id = 53458 with RAPIDDataset(path_to_rapid_qout) as qout_nc: river_index = qout_nc.get_river_index(river_id) """

        try:
            return np.where(self.get_river_id_array() == river_id)[0][0]
        except IndexError:
            raise IndexError("ERROR: River ID {0} not found in dataset "
                             "...".format(river_id))