Function group_window_expr_by_sort_keys

datafusion/expr/src/utils.rs:622–644

Group a slice of window expression expr by their order by expressions

(
    window_expr: impl IntoIterator<Item = Expr>,
)

/// Group a slice of window expression expr by their order by expressions
pub fn group_window_expr_by_sort_keys(
    window_expr: impl IntoIterator<Item = Expr>,
) -> Result<Vec<(WindowSortKey, Vec<Expr>)>> {
    let mut result = vec![];
    window_expr.into_iter().try_for_each(|expr| match &expr {
        Expr::WindowFunction(window_fun) => {
            let WindowFunctionParams{ partition_by, order_by, ..} = &window_fun.as_ref().params;
            let sort_key = generate_sort_key(partition_by, order_by)?;
            if let Some((_, values)) = result.iter_mut().find(
                |group: &&mut (WindowSortKey, Vec<Expr>)| matches!(group, (key, _) if *key == sort_key),
            ) {
                values.push(expr);
            } else {
                result.push((sort_key, vec![expr]))
            }
            Ok(())
        }
        other => internal_err!(
            "Impossibly got non-window expr {other:?}"
        ),
    })?;
    Ok(result)
}

/// Collect all deeply nested `Expr::AggregateFunction`.
/// They are returned in order of occurrence (depth