jorisvandenbossche commented on code in PR #41956:
URL: https://github.com/apache/arrow/pull/41956#discussion_r1625871222
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cpp/src/arrow/array/array_nested.cc:
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@@ -847,14 +847,13 @@ Result<std::shared_ptr<Array>>
MapArray::FromArraysInternal(
const auto& typed_offsets = checked_cast<const OffsetArrayType&>(*offsets);
BufferVector buffers;
- int64_t null_count;
- if (null_bitmap != nullptr) {
- buffers = BufferVector({std::move(null_bitmap), typed_offsets.values()});
- null_count = null_bitmap->size();
- } else {
- buffers = BufferVector({null_bitmap, typed_offsets.values()});
- null_count = 0;
+ buffers.resize(2);
+ int64_t null_count = 0;
+ if (null_bitmap) {
+ buffers[0] = std::move(null_bitmap);
+ null_count = internal::CountSetBits(null_bitmap->data(), 0,
offsets->length());
Review Comment:
As mentioned in the other PR, you want to count the "unset" bits. I think
typically that is done by doing `null_count = length - CountSetBits(..)`. But,
maybe we can also just keep this defined at `-1` (as it was before) to postpone
the actual count.
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