pub fn push(&mut self, name: &str, series: Series) {
        if !self.ics.is_empty() {
            assert_eq!(
                self.ics.iter().find(|x| x.as_str() == name),
                None,
                "Repetitive index!"
            );
        }
        self.ics.push(name.to_string());
        self.data.push(series);
    }
Push new pair of head, Series to DataFrame
src/structure/dataframe.rs