polars_core/frame/
top_k.rs

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use super::*;
use crate::prelude::sort::arg_bottom_k::_arg_bottom_k;

impl DataFrame {
    pub(crate) fn bottom_k_impl(
        &self,
        k: usize,
        by_column: Vec<Column>,
        mut sort_options: SortMultipleOptions,
    ) -> PolarsResult<DataFrame> {
        let first_descending = sort_options.descending[0];
        let first_by_column = by_column[0].name().to_string();

        let idx = _arg_bottom_k(k, &by_column, &mut sort_options)?;

        let mut df = unsafe { self.take_unchecked(&idx.into_inner()) };

        // Mark the first sort column as sorted
        // if the column did not exists it is ok, because we sorted by an expression
        // not present in the dataframe
        let _ = df.apply(&first_by_column, |s| {
            let mut s = s.clone();
            if first_descending {
                s.set_sorted_flag(IsSorted::Descending)
            } else {
                s.set_sorted_flag(IsSorted::Ascending)
            }
            s
        });
        Ok(df)
    }
}