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From "Julien Le Dem (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ARROW-81) [Format] Add a Category logical type (distinct from dictionary-encoding)
Date Sat, 20 Aug 2016 04:53:20 GMT

    [ https://issues.apache.org/jira/browse/ARROW-81?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15429218#comment-15429218
] 

Julien Le Dem commented on ARROW-81:
------------------------------------

[~wesmckinn] and [~emkornfield@gmail.com]: the proposal of adding categorical_type fiel to
Field sounds good to me.
when it is set then it is required that the field is dictionary encoded.

> [Format] Add a Category logical type (distinct from dictionary-encoding)
> ------------------------------------------------------------------------
>
>                 Key: ARROW-81
>                 URL: https://issues.apache.org/jira/browse/ARROW-81
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: C++
>            Reporter: Wes McKinney
>            Assignee: Wes McKinney
>
> A Category (or "factor") is a dictionary-encoded array whose dictionary has semantic
meaning. The data consists of
> - An array of integer "codes"
> - A child array of some other type, known as the "categories" or "levels" of the array.
Typically there is an "ordered" boolean flag indicating whether the order of the categories
is meaningful.
> Category/factor types are used in a number of common statistical analyses. See, for example,
http://www.voteview.com/R_Ordered_Logistic_or_Probit_Regression.htm. It is a basic requirement
for Python and R, at least, as Arrow C++ consumers, to have this type. Separately, we should
consider what is necessary to be able to transmit category data in IPCs -- possible an expansion
of the Arrow format. 



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