Jefffrey commented on code in PR #10292:
URL: https://github.com/apache/arrow-rs/pull/10292#discussion_r3529589129
##########
arrow-buffer/src/buffer/run.rs:
##########
@@ -421,4 +432,53 @@ mod tests {
let sliced_values: Vec<i32> = sliced.sliced_values().collect();
assert_eq!(sliced_values, &[2]);
}
+
+ #[test]
+ fn test_compact_slicing() {
+ // {} represents a logical slice within physically expanded []
+ // [{A, A, A, A, B, B, B, B, C, C, C, C}]
+ let buffer = RunEndBuffer::<i32>::new(vec![4, 8, 12].into(), 0, 12);
+
+ // zero slice
+ let slice = buffer.slice(0, 0);
+ assert_eq!(slice.len(), 0);
+ assert_eq!(slice.offset(), 0);
+ assert_eq!(slice.values(), &[4]);
+
+ // compact start only
+ // [B, B, B, B, B, B, {B, B, C, C, C, C}]
+ let slice = buffer.slice(6, 6);
+ assert_eq!(slice.len(), 6);
+ assert_eq!(slice.offset(), 6);
Review Comment:
i realized my initial version of the PR incorrectly adjusted the offset when
that wasnt needed; by removing the first physical value its as if the first run
was consumed by the following run since we always list run lengths; that is
```
[4, 8] -> AAAABBBB
[8] -> {BBBB}BBBB
```
- where `{BBBB}` used to be a separate run but is now folded into the first
run; this shouldnt matter as our logical offset points beyond it anyway
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