Method truncate

datafusion/physical-expr-common/src/sort_expr.rs:418–427

Truncates the `LexOrdering`, keeping only the first `len` elements. Returns `true` if truncation made a change, `false` otherwise. Negative cases happen in two scenarios: (1) When `len` is greater than or equal to the number of expressions inside this `LexOrdering`, making truncation a no-op, or (2) when `len` is `0`, making truncation impossible.

(&mut self, len: usize)

    /// to the number of expressions inside this `LexOrdering`, making truncation
    /// a no-op, or (2) when `len` is `0`, making truncation impossible.
    pub fn truncate(&mut self, len: usize) -> bool {
        if len == 0 || len >= self.exprs.len() {
            return false;
        }
        for PhysicalSortExpr { expr, .. } in self.exprs[len..].iter() {
            self.set.swap_remove(expr);
        }
        self.exprs.truncate(len);
        true
    }

    /// Check if reversing this ordering would satisfy another ordering requirement.
    ///