fix a bug in length dedup optimization

Author: kaikalii

src/algorithm/monadic/mod.rs

@@ -1547,6 +1547,9 @@ impl<T: ArrayValue> Array<T> {
     }
     /// Count the number of unique rows in the array
     pub fn count_unique(&self) -> usize {
+        if self.element_count() == 0 && self.row_count() > 0 {
+            return 1;
+        }
         let mut seen = HashSet::new();
         self.row_slices()
             .filter(|row| seen.insert(ArrayCmpSlice(row)))

tests/optimized.ua

@@ -129,6 +129,9 @@ F ← /◇⊂
 ⍤⤙≍ ⊃(⧻∘⊚|⧻⊚) [1 0 3]
 ⍤⤙≍ ⊃(⧻∘⊚|⧻⊚) [1 0 1 0 1 0 1]
 
+# Count unique
+⍤⤙≍ ⊃(⧻∘◴|⧻◴) °△ 1_0
+
 # Depth deshape
 ⍤⤙≍ ⊃≡(♭∘)≡♭ °△2_2_3_3
 ⍤⤙≍ ⊃≡(♭₀∘)≡♭₀ °△2_2_3_3