alamb commented on code in PR #18424:
URL: https://github.com/apache/datafusion/pull/18424#discussion_r2486523946
##########
datafusion/functions-nested/src/reverse.rs:
##########
@@ -183,6 +195,72 @@ fn general_array_reverse<O: OffsetSizeTrait +
TryFrom<i64>>(
)?))
}
+fn list_view_reverse<O: OffsetSizeTrait + TryFrom<i64>>(
+ array: &GenericListViewArray<O>,
+ field: &FieldRef,
+) -> Result<ArrayRef> {
+ let offsets = array.offsets();
+ let values = array.values();
+ let sizes = array.sizes();
+
+ // Construct indices, sizes and offsets for the reversed array by
iterating over
+ // the list view array in the logical order, and reversing the order of
the elements.
+ // We end up with a list view array where the elements are in order,
+ // even if the original array had elements out of order.
+ let mut indices: Vec<O> = Vec::with_capacity(values.len());
+ let mut new_sizes = Vec::with_capacity(sizes.len());
+ let mut new_offsets: Vec<O> = Vec::with_capacity(offsets.len());
+ // Add the offset of the first array
+ new_offsets.push(O::zero());
Review Comment:
Per https://arrow.apache.org/docs/format/Columnar.html#listview-layout
the offsets for a ListView are simply the offsets into the child array
So I think the fastest/ simplest implementation is going to be
1. reverse both the offsets and lengths array
2. reverse the nulls array
3. create a new list array with the new offsets/lengths/nulls and child
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