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https://issues.apache.org/jira/browse/ARROW-1559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16252909#comment-16252909
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ASF GitHub Bot commented on ARROW-1559:
---------------------------------------
wesm commented on a change in pull request #1266: ARROW-1559: [C++] Add Unique
kernel and refactor DictionaryBuilder to be a stateful kernel
URL: https://github.com/apache/arrow/pull/1266#discussion_r151027415
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File path: cpp/src/arrow/array.cc
##########
@@ -92,7 +92,7 @@ static inline std::shared_ptr<ArrayData> SliceData(const
ArrayData& data, int64_
auto new_data = data.ShallowCopy();
new_data->length = length;
new_data->offset = offset;
- new_data->null_count = kUnknownNullCount;
+ new_data->null_count = data.null_count != 0 ? kUnknownNullCount : 0;
Review comment:
This is a helpful optimization -- if you know your null count is already 0,
no need to keep thinking it's unknown
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> [C++] Kernel implementations for "unique" (compute distinct elements of array)
> ------------------------------------------------------------------------------
>
> Key: ARROW-1559
> URL: https://issues.apache.org/jira/browse/ARROW-1559
> Project: Apache Arrow
> Issue Type: New Feature
> Components: C++
> Reporter: Wes McKinney
> Assignee: Uwe L. Korn
> Labels: Analytics, pull-request-available
> Fix For: 0.8.0
>
>
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