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https://issues.apache.org/jira/browse/ARROW-2328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16410081#comment-16410081
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ASF GitHub Bot commented on ARROW-2328:
---------------------------------------
xhochy commented on a change in pull request #1766: ARROW-2328: [C++] Writing a
slice with feather ignores the offset.
URL: https://github.com/apache/arrow/pull/1766#discussion_r176529987
##########
File path: cpp/src/arrow/ipc/feather.cc
##########
@@ -558,8 +577,18 @@ class TableWriter::TableWriterImpl : public ArrayVisitor {
// byte boundary, and we write this much data into the stream
int64_t null_bitmap_size =
GetOutputLength(BitUtil::BytesForBits(values.length()));
if (values.null_bitmap()) {
- RETURN_NOT_OK(WritePadded(stream_.get(), values.null_bitmap()->data(),
- null_bitmap_size, &bytes_written));
+ auto null_bitmap = values.null_bitmap();
+ if (values.offset() > 0) {
+ if (!pool_) {
+ return Status::Invalid(
+ "Require memory pol to write array slice (i.e. offset > 0)
with nulls.");
+ }
+ RETURN_NOT_OK(GetTruncatedBitmap(values.offset(), values.length(),
null_bitmap,
+ pool_, &null_bitmap));
+ }
+
+ RETURN_NOT_OK(WritePadded(stream_.get(), null_bitmap->data(),
null_bitmap_size,
Review comment:
Wouldn't it be better to extend `WritePadded` or write a second version of
it that can handle bit-offsets? Using that way we could avoid the memory
allocation for `GetTruncatedBitmap` above.
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> Writing a slice with feather ignores the offset
> -----------------------------------------------
>
> Key: ARROW-2328
> URL: https://issues.apache.org/jira/browse/ARROW-2328
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Affects Versions: 0.8.0
> Reporter: Adrian
> Priority: Major
> Labels: pull-request-available
> Fix For: 0.10.0
>
> Original Estimate: 0.5h
> Remaining Estimate: 0.5h
>
> Writing a slice from row n of length m of an array to feather would write the
> first m rows, instead of the rows starting at n.
> The null bitmap also ends up misaligned. Also tested and fixed in the pull
> request below.
> I've created a pull request with tests and fix here:
> [Pullrequest#1766|https://github.com/apache/arrow/pull/1766]
>
>
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