Rich-T-kid commented on code in PR #10323:
URL: https://github.com/apache/arrow-rs/pull/10323#discussion_r3567332408
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arrow-data/src/transform/mod.rs:
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@@ -195,7 +195,10 @@ impl std::fmt::Debug for MutableArrayData<'_> {
fn build_extend_dictionary(array: &ArrayData, offset: usize, max: usize) ->
Option<Extend<'_>> {
macro_rules! validate_and_build {
($dt: ty) => {{
- let _: $dt = max.try_into().ok()?;
+ // `max` is the merged dictionary length; the largest key index is
+ // `max - 1`, so the key type only needs to hold `max - 1` (e.g.
256
+ // values use keys 0..=255, which fit in u8).
+ let _: $dt = max.saturating_sub(1).try_into().ok()?;
Review Comment:
nice catch
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