[jira] Commented: (MAHOUT-421) Item similarity in AbstractSimilarity always centers data

["Emerson Murphy-HIll (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12880969#action_12880969 ] 

Emerson Murphy-HIll commented on MAHOUT-421:
--------------------------------------------

Bleh. Sorry. I'm getting myself confused. In AbstractSimilarity, userSimilarity *always* centers the data, whereas itemSimilarity is conditional. The problem, then, is with userSimilarity.

> Item similarity in AbstractSimilarity always centers data
> ---------------------------------------------------------
>
>                 Key: MAHOUT-421
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-421
>             Project: Mahout
>          Issue Type: Bug
>          Components: Collaborative Filtering
>            Reporter: Emerson Murphy-HIll
>
> I'm trying to use UncenteredCosineSimilarity. When calculating similarity between users in AbstractSimilarity>>itemSimilarity, there's a condition to determine whether to center the data:
> double result;
> if (centerData) {
>   ... get result with centering
> } else {
>    ... get result without
> }
>    
> In AbstractSimilarity>>itemSimilarity, there's no conditional. It *always* centers the data. Shouldn't it only center the data when centerData is true?

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