okhsunrog commented on code in PR #10927:
URL: https://github.com/apache/arrow-rs/pull/10927#discussion_r3905581761
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arrow-select/src/concat.rs:
##########
@@ -1708,6 +1708,124 @@ mod tests {
assert_eq!(array.logical_null_count(), 10);
}
+ #[test]
+ fn concat_string_view_dictionary_merges_duplicate_values() {
+ // Two independently-built `Dictionary<UInt8, Utf8View>` arrays
holding the
+ // same 200 distinct values. Naively concatenating their dictionaries
yields
+ // 400 entries, which overflows the u8 key range, but the distinct
values do
+ // fit -- so the values must be merged and deduplicated instead. This
mirrors
+ // a `Dictionary<UInt16, Utf8View>` column read in several partitions,
each
+ // building its own dictionary, and then combined.
+ let dict = |offset: usize| {
+ let values: StringViewArray = (0..200).map(|i|
Some(format!("v{i}"))).collect();
+ let keys = UInt8Array::from_iter_values((0..200).map(|i| (i +
offset) as u8 % 200));
+ DictionaryArray::<UInt8Type>::new(keys, Arc::new(values))
+ };
+ let (a, b) = (dict(0), dict(7));
+
+ let combined = concat(&[&a, &b]).unwrap();
+ let combined = combined.as_dictionary::<UInt8Type>();
+
+ assert_eq!(combined.len(), 400);
+ assert_eq!(combined.values().data_type(), &DataType::Utf8View);
+ assert!(combined.values().len() < 400);
Review Comment:
It is 251 here, not 200. With only two dictionaries the best-effort interner
has enough buckets to do the merge on its own, so the exact retry never runs
and 51 duplicates survive. The property worth asserting is that the result fits
the key type, so I went with
`assert!(u8::try_from(combined.values().len()).is_ok())` and said why in a
comment. The test still checks every key resolves to its original value, which
is the real guarantee.
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