sdf-jkl commented on code in PR #18363:
URL: https://github.com/apache/datafusion/pull/18363#discussion_r2475488549
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datafusion/functions-nested/src/flatten.rs:
##########
@@ -154,7 +158,32 @@ pub fn flatten_inner(args: &[ArrayRef]) ->
Result<ArrayRef> {
Ok(Arc::new(flattened_array) as ArrayRef)
}
LargeList(_) => {
- exec_err!("flatten does not support type '{:?}'",
array.data_type())?
+ let (inner_field, inner_offsets, inner_values, _) =
+ as_large_list_array(&values)?.clone().into_parts();
+ // Try to downcast the inner offsets to i32
+ match downcast_i64_inner_to_i32(&inner_offsets, &offsets) {
+ Ok(i32offsets) => {
+ let flattened_array = GenericListArray::<i32>::new(
+ inner_field,
+ i32offsets,
+ inner_values,
+ nulls,
+ );
+ Ok(Arc::new(flattened_array) as ArrayRef)
+ }
+ // If downcast fails we keep the offsets as is
+ Err(_) => {
+ // Fallback: keep i64 offsets → LargeList<i64>
+ let i64offsets = keep_offsets_i64(inner_offsets,
offsets);
+ let flattened_array = GenericListArray::<i64>::new(
+ inner_field,
+ i64offsets,
+ inner_values,
+ nulls,
+ );
+ Ok(Arc::new(flattened_array) as ArrayRef)
Review Comment:
I was looking at @Jefffrey's original comment suggesting that we should try
to downcast it `i32` returning a `ListArray` and alternatively return a
`LargeListArray` if downcast is not possible.
He also mentioned that upcasting the parent offsets to `LargeListArray`
blindly would be inefficient and undesirable.
I wanted to see if it's possible to infer the possibility of downcasting the
inner array offsets within the `return_type` function. Then return the matching
output type.
We could do it by checking if: `inner_offsets.last() <= i32::MAX`
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