'Update selected dataframe after a completed batch
Parameters
df_name : str
Selected dataframe name needs to be modified.'

def _process_batch(self, param, df_name):

    if (param.eval_metric is not None):
        metrics = dict(param.eval_metric.get_name_value())
        param.eval_metric.reset()
    else:
        metrics = {}
    metrics['elapsed'] = (datetime.datetime.now() - self.start_time)
    for (key, value) in metrics.items():
        if (not self._data[df_name].has_key(key)):
            self._data[df_name][key] = []
        self._data[df_name][key].append(value)
