dqkqd commented on code in PR #8735:
URL: https://github.com/apache/arrow-rs/pull/8735#discussion_r2556005600
##########
arrow-cast/src/cast/list.rs:
##########
@@ -160,6 +169,70 @@ pub(crate) fn cast_list_values<O: OffsetSizeTrait>(
)?))
}
+/// Helper function to cast a list view to a list
+pub(crate) fn cast_list_view_to_list<O: OffsetSizeTrait>(
+ array: &dyn Array,
+ to: &FieldRef,
+ cast_options: &CastOptions,
+) -> Result<ArrayRef, ArrowError> {
+ let list_view = array.as_list_view::<O>();
+ let list_view_offsets = list_view.offsets();
+ let sizes = list_view.sizes();
+ let source_values = list_view.values();
+
+ // Construct the indices and offsets for the new list array by iterating
over the list view subarrays
+ let mut indices = Vec::with_capacity(list_view.values().len());
+ let mut offsets = Vec::with_capacity(list_view.len() + 1);
+ // Add the offset for the first subarray
+ offsets.push(O::usize_as(0));
+ for i in 0..list_view.len() {
+ // For each subarray, add the indices of the values to take
+ let offset = list_view_offsets[i].as_usize();
+ let size = sizes[i].as_usize();
+ let end = offset + size;
+ for j in offset..end {
+ indices.push(j as i32);
+ }
+ // Add the offset for the next subarray
+ offsets.push(O::usize_as(indices.len()));
+ }
+
+ // Take the values from the source values using the indices, creating a
new array
+ let values = arrow_select::take::take(source_values,
&Int32Array::from(indices), None)?;
Review Comment:
> I believe MutableArrayData is not as performant as take. Since we know
upfront what indices we need, I think take is the right call here.
Thank you, I did not know this. I thought it would be better to just use
`MutableArrayData` because we are manually building the `indicies` anyway.
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