pub fn pivot_stable<I0, S0, I1, S1, I2, S2>(
    df: &DataFrame,
    values: I0,
    index: I1,
    columns: I2,
    sort_columns: bool,
    agg_expr: Option<Expr>,
    separator: Option<&str>
) -> PolarsResult<DataFrame>where
    I0: IntoIterator<Item = S0>,
    S0: AsRef<str>,
    I1: IntoIterator<Item = S1>,
    S1: AsRef<str>,
    I2: IntoIterator<Item = S2>,
    S2: AsRef<str>,
Available on crate feature pivot only.