wjones127 commented on code in PR #5081:
URL: https://github.com/apache/arrow-rs/pull/5081#discussion_r1397648349
##########
arrow-cast/src/cast.rs:
##########
@@ -3206,6 +3221,73 @@ where
Ok(Arc::new(list))
}
+fn cast_list_to_fixed_size_list<OffsetSize>(
+ array: &GenericListArray<OffsetSize>,
+ field: &Arc<Field>,
+ size: i32,
+ cast_options: &CastOptions,
+) -> Result<ArrayRef, ArrowError>
+where
+ OffsetSize: OffsetSizeTrait,
+{
+ let cap = array.len() * size as usize;
+
+ let mut nulls = (cast_options.safe || array.null_count() != 0).then(|| {
+ let mut buffer = BooleanBufferBuilder::new(array.len());
+ match array.nulls() {
+ Some(n) => buffer.append_buffer(n.inner()),
+ None => buffer.append_n(array.len(), true),
+ }
+ buffer
+ });
+
+ // Nulls in FixedSizeListArray take up space and so we must pad the values
+ let values = array.values().to_data();
+ let mut mutable = MutableArrayData::new(vec![&values], cast_options.safe,
cap);
+ let mut last_pos = 0;
+ for (idx, w) in array.offsets().windows(2).enumerate() {
+ let start_pos = w[0].as_usize();
+ let end_pos = w[1].as_usize();
+ let len = end_pos - start_pos;
+
+ if len != size as usize {
+ if cast_options.safe || array.is_null(idx) {
+ // Pad with nulls
+ if last_pos != start_pos {
+ mutable.extend(0, last_pos, start_pos);
+ }
+ mutable.extend_nulls(size as _);
+ nulls.as_mut().unwrap().set_bit(idx, false);
+ last_pos = end_pos
Review Comment:
Sorry, I see how this works now. I misunderstood how `MutableArrayData`
works, but re-reading the docs this makes sense now.
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