code: def load_mpower_data(filename, convert_times=1000000000.0):
      
      raw_data = pd.read_json(filename)
      date_times = pd.to_datetime(raw_data.timestamp * convert_times - raw_data.timestamp[0] * convert_times)
      time_difference = (raw_data.timestamp - raw_data.timestamp[0])
      time_difference = time_difference.values
      magnitude_sum_acceleration = \
          np.sqrt(raw_data.x.values ** 2 + raw_data.y.values ** 2 + raw_data.z.values ** 2)
      data = {'td': time_difference, 'x': raw_data.x.values, 'y': raw_data.y.values,
              'z': raw_data.z.values, 'mag_sum_acc': magnitude_sum_acceleration}
      data_frame = pd.DataFrame(data, index=date_times, columns=['td', 'x', 'y', 'z', 'mag_sum_acc'])
      return data_frame
docs: This method loads data in the `mpower <https://www.synapse.org/#!Synapse:syn4993293/wiki/247859>`_ format
          
          The format is like: 
          
          .. code-block:: json
  
              [
                 {
                    "timestamp":19298.67999479167,
                    "x": ... ,
                    "y": ...,
                    "z": ...,
                 },
                 {...},
                 {...}
              ]
  
          :param filename: The path to load data from
          :type filename: string
          :param convert_times: Convert times. The default is from from nanoseconds to seconds.
          :type convert_times: float