pitrou commented on code in PR #50423:
URL: https://github.com/apache/arrow/pull/50423#discussion_r3628711154
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cpp/src/arrow/compute/kernels/pivot_internal.cc:
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@@ -75,6 +79,19 @@ struct ConcretePivotWiderKeyMapper : public
PivotWiderKeyMapper {
}
Unreachable("Grouper doesn't agree with std::unordered_set");
}
+ // GH-48679: the fast grouper implementation may produce non-monotonic
+ // group ids, for example [0,1,2,4,3] rather than [0,1,2,3,4].
+ // Therefore, we need to produce a mapping a mapping of group ids to key
indices.
+ auto key_indices_to_group_ids_data = key_indices_to_group_ids.array();
+ // InversePermutation doesn't allow unsigned integers, patch to signed.
+ DCHECK_EQ(key_indices_to_group_ids_data->type->id(), Type::UINT32);
+ key_indices_to_group_ids_data->type = int32();
+ ARROW_ASSIGN_OR_RAISE(group_ids_to_key_indices_,
+ InversePermutation(key_indices_to_group_ids_data,
+
InversePermutationOptions::Defaults(), ctx));
+ group_ids_to_key_indices_.array()->type = uint32();
Review Comment:
Will do!
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