[GitHub] [arrow] pitrou commented on a diff in pull request #13646: ARROW-17096: [C++][Compute] Fix mode kernel error on boolean array

[GitBox <gi...@apache.org>]

pitrou commented on code in PR #13646:
URL: https://github.com/apache/arrow/pull/13646#discussion_r924232114


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cpp/src/arrow/compute/kernels/aggregate_mode.cc:
##########
@@ -201,18 +203,21 @@ struct CountModer<BooleanType> {
     const int64_t distinct_values = (this->counts[0] != 0) + (this->counts[1] != 0);
     const int64_t n = std::min(options.n, distinct_values);
 
-    bool* mode_buffer;
+    uint8_t* mode_buffer;
     int64_t* count_buffer;
     ARROW_ASSIGN_OR_RAISE(std::tie(mode_buffer, count_buffer),
-                          PrepareOutput<BooleanType>(n, ctx, type, out));
+                          (PrepareOutput<BooleanType, uint8_t>(n, ctx, type, out)));
 
     if (n >= 1) {
-      const bool index = counts[1] > counts[0];
-      mode_buffer[0] = index;
-      count_buffer[0] = counts[index];
+      // at most two bits are useful in mode buffer
+      bit_util::ClearBitmap(mode_buffer, 0, 8);

Review Comment:
   Simply `mode_buffer[0] = 0`?



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