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https://issues.apache.org/jira/browse/ARROW-1741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16340458#comment-16340458
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Wes McKinney commented on ARROW-1741:
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I'm not sure about the right API for this yet, since this feature is not yet
needed for anything right now (I have not set a "Fix Version" yet). When we
implement array vector comparisons (e.g. {{a == b}}) this will be useful to
enable dictionary-encoded arrays to be compared if one dictionary is contained
in another.
> [C++] Comparison function for DictionaryArray to determine if indices are
> "compatible"
> --------------------------------------------------------------------------------------
>
> Key: ARROW-1741
> URL: https://issues.apache.org/jira/browse/ARROW-1741
> Project: Apache Arrow
> Issue Type: New Feature
> Components: C++
> Reporter: Wes McKinney
> Priority: Major
>
> For example, if one array's dictionary is larger than the other, but the
> overlapping beginning portion is the same, then the respective dictionary
> indices correspond to the same values. Therefore, in analytics, one may
> choose to drop the smaller dictionary in favor of the larger dictionary, and
> this need not incur any computational overhead (beyond comparing the
> dictionary prefixes -- there may be some way to engineer "dictionary lineage"
> to make this comparison even cheaper)
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