Jefffrey commented on code in PR #9023:
URL: https://github.com/apache/arrow-datafusion/pull/9023#discussion_r1468670417
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datafusion/physical-expr/src/array_expressions.rs:
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@@ -2766,6 +2766,72 @@ where
)?))
}
+/// array_reverse SQL function
+pub fn array_reverse(arg: &[ArrayRef]) -> Result<ArrayRef> {
+ if arg.len() != 1 {
+ return exec_err!("array_reverse needs one argument");
+ }
+
+ match &arg[0].data_type() {
+ DataType::List(field) => {
+ let array = as_list_array(&arg[0])?;
+ general_array_reverse::<i32>(array, &field)
+ }
+ DataType::LargeList(field) => {
+ let array = as_large_list_array(&arg[0])?;
+ general_array_reverse::<i64>(array, &field)
+ }
+ DataType::Null => Ok(arg[0].clone()),
+ array_type => exec_err!("array_reverse does not support type
'{array_type:?}'."),
+ }
+}
+
+fn general_array_reverse<O: OffsetSizeTrait>(
+ array: &GenericListArray<O>,
+ field: &FieldRef,
+) -> Result<ArrayRef>
+where
+ O: TryFrom<i64>,
+{
+ let values = array.values();
+ let original_data = values.to_data();
+ let capacity = Capacities::Array(original_data.len());
+ let mut offsets = vec![O::usize_as(0)];
+ let mut nulls = vec![];
+ let mut mutable =
+ MutableArrayData::with_capacities(vec![&original_data], false,
capacity);
+
+ for (row_index, offset_window) in array.offsets().windows(2).enumerate() {
+ let start = offset_window[0];
+ let end = offset_window[1];
+
+ let mut index = end - O::one();
+ let mut cnt = 0;
+ let stride: O = (-1 as i64).try_into().map_err(|_| {
+ internal_datafusion_err!("array_reverse: failed to convert size to
i64")
+ })?;
+ while index >= start {
+ mutable.extend(0, index.to_usize().unwrap(),
index.to_usize().unwrap() + 1);
+ index += stride;
+ cnt += 1;
+ }
+ offsets.push(offsets[row_index] + O::usize_as(cnt));
+ if cnt == 0 {
+ nulls.push(false);
+ } else {
+ nulls.push(true);
+ }
Review Comment:
I'm not sure we can rely on `cnt` being zero to indicate a null?
According to arrow-rs doc for GenericListArray:
https://github.com/apache/arrow-rs/blob/5117b38d99f23498f6b87e23efbe06a841c63b0b/arrow-array/src/array/list_array.rs#L99-L123
Nulls could take up a non-zero slot of offsets.
Please let me know if my understanding is incorrect on this account
:sweat_smile:
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