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From "Micah Kornfield (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ARROW-81) [Format] Add a Category logical type (distinct from dictionary-encoding)
Date Sat, 20 Aug 2016 06:24:20 GMT

    [ https://issues.apache.org/jira/browse/ARROW-81?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15429254#comment-15429254
] 

Micah Kornfield commented on ARROW-81:
--------------------------------------

Do we want to make an exception for requiring dictionary encoding for Categorical[ints]? 

> [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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