Jefffrey commented on code in PR #9607:
URL: https://github.com/apache/arrow-rs/pull/9607#discussion_r2994076190
##########
arrow-data/src/transform/union.rs:
##########
@@ -68,10 +69,43 @@ pub(super) fn build_extend_dense(array: &ArrayData) ->
Extend<'_> {
)
}
-pub(super) fn extend_nulls_dense(_mutable: &mut _MutableArrayData, _len:
usize) {
- panic!("cannot call extend_nulls on UnionArray as cannot infer type");
+pub(super) fn extend_nulls_dense(mutable: &mut _MutableArrayData, len: usize) {
+ let DataType::Union(fields, _) = &mutable.data_type else {
+ unreachable!()
+ };
+ let first_type_id = fields
+ .iter()
+ .next()
+ .expect("union must have at least one field")
+ .0;
+
+ // Extend type_ids buffer
+ mutable.buffer1.extend_from_slice(&vec![first_type_id; len]);
+
+ // Dense: extend offsets pointing into the first child, then extend nulls
in that child
+ let child_offset = mutable.child_data[0].len();
+ mutable
+ .buffer2
+ .extend((0..len).map(|i| (child_offset + i) as i32));
Review Comment:
```suggestion
let (start, end) = (child_offset as i32, (child_offset + len) as i32);
mutable.buffer2.extend(start..end);
```
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