Get the date histogram aggregations.

        :param dataframe: if true, return a pandas.DataFrame object

def timeseries(self, dataframe=False):
        """Get the date histogram aggregations.

        :param dataframe: if true, return a pandas.DataFrame object
        """

        self.query.by_period()
        ts = super().timeseries(dataframe=dataframe)
        ts['value'] = ts['value'].apply(lambda x: float("%.2f" % x))
        return ts