fix grouped sum index

Author: onursatici

vortex-array/src/aggregate_fn/accumulator_grouped.rs

@@ -229,11 +229,12 @@ impl<V: AggregateFnVTable> GroupedAccumulator<V> {
         )?;
         let mut states = builder_with_capacity(&self.partial_dtype, offsets.len());
 
-        for (offset, size) in offsets.iter().zip(sizes.iter()) {
+        for (i, (offset, size)) in offsets.iter().zip(sizes.iter()).enumerate() {
             let offset = offset.to_usize().vortex_expect("Offset value is not usize");
             let size = size.to_usize().vortex_expect("Size value is not usize");
 
-            if validity.value(offset) {
+            // validity is for the outer list view, so it must be indexed with `i`
+            if validity.value(i) {
                 let group = elements.slice(offset..offset + size)?;
                 accumulator.accumulate(&group, ctx)?;
                 states.append_scalar(&accumulator.flush()?)?;

vortex-array/src/aggregate_fn/fns/sum/mod.rs

@@ -347,6 +347,7 @@ mod tests {
     use crate::arrays::ConstantArray;
     use crate::arrays::DecimalArray;
     use crate::arrays::FixedSizeListArray;
+    use crate::arrays::ListViewArray;
     use crate::arrays::PrimitiveArray;
     use crate::assert_arrays_eq;
     use crate::dtype::DType;
@@ -616,6 +617,25 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn grouped_sum_listview_out_of_order_offsets_with_null_group() -> VortexResult<()> {
+        let elements =
+            PrimitiveArray::new(buffer![100i32, 200, 300], Validity::NonNullable).into_array();
+        let offsets = PrimitiveArray::new(buffer![2i32, 0, 1], Validity::NonNullable).into_array();
+        let sizes = PrimitiveArray::new(buffer![1i32, 1, 1], Validity::NonNullable).into_array();
+        let validity = Validity::from_iter([true, false, true]);
+        let groups = ListViewArray::try_new(elements, offsets, sizes, validity)?.into_array();
+
+        let elem_dtype = DType::Primitive(PType::I32, Nullability::NonNullable);
+        let result = run_grouped_sum(&groups, &elem_dtype)?;
+
+        // group 0 -> elements[2..3] = 300; group 1 -> null; group 2 -> elements[1..2] = 200.
+        let expected =
+            PrimitiveArray::from_option_iter([Some(300i64), None, Some(200i64)]).into_array();
+        assert_arrays_eq!(&result, &expected);
+        Ok(())
+    }
+
     // Chunked array tests
 
     #[test]