'Append new metrics to selected dataframes.
Parameters
metrics : metric.EvalMetric
New metrics to be added.
df_name : str
Name of the dataframe to be modified.'

def append_metrics(self, metrics, df_name):

    dataframe = self._dataframes[df_name]
    _add_new_columns(dataframe, metrics)
    dataframe.loc[len(dataframe)] = metrics
