Function collect_columns

datafusion/physical-expr/src/utils/mod.rs:286–297

Recursively extract referenced [`Column`]s within a [`PhysicalExpr`].

(expr: &Arc<dyn PhysicalExpr>)

/// Recursively extract referenced [`Column`]s within a [`PhysicalExpr`].
pub fn collect_columns(expr: &Arc<dyn PhysicalExpr>) -> HashSet<Column> {
    let mut columns = HashSet::<Column>::new();
    expr.apply(|expr| {
        if let Some(column) = expr.downcast_ref::<Column>() {
            columns.get_or_insert_with(column, |c| c.clone());
        }
        Ok(TreeNodeRecursion::Continue)
    })
    // pre_visit always returns OK, so this will always too
    .expect("no way to return error during recursion");
    columns
}

/// Re-assign indices of [`Column`]s within the given [`PhysicalExpr`] according to
/// the provided [`Schema`].