chore: Use ArrayBuilder to build the array #564
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He-Pin
commented
Dec 9, 2025
JoshRosen
reviewed
Dec 21, 2025
| for (v <- arrValue) { | ||
| if (out.isEmpty) { | ||
| out.append(v) | ||
| val outResult = out.result() |
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I think that this change is introducing an O(n^2) bug because now we're making a fresh copy of the array on every loop iteration.
I've opened #575 with a suggested fix.
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Yes, we need just use the length to fix this.
stephenamar-db
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Dec 22, 2025
…ns (#575) This PR implements two performance optimizations in `uniqueArr`: - **Fix an O(n^2) performance bug**: #564 changed this code to call `out.result()` on every loop iteration, resulting in copying of an `O(n)` sized array on each loop iteration. We can avoid this by keeping a reference to the last output element. - **Avoid duplicate keyF evaluations**: in the old code, each loop iteration would repeat the `keyF` evaluation for the last element of the output array; the new code calls `keyF` exactly once per element by maintaining a `lastAddedKey` variable during the loop. - This is similar in spirit to #245 Claude (Opus 4.5) spotted the O(n^2) bug and designed that part of the fix. I spotted the duplicate keyF evaluation and suggested this fix (plus the switch to a `while` loop). Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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The ArrayBuffer#toArray will do another copy.