[jira] [Commented] (MAHOUT-1545) Creating holdout sets with seq2sparse and split

["Sebastian Schelter (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-1545?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13989285#comment-13989285 ] 

Sebastian Schelter commented on MAHOUT-1545:
--------------------------------------------

Good point. We should ensure to get this correct in the new preprocessing/vectorization code.

> Creating holdout sets with seq2sparse and split
> -----------------------------------------------
>
>                 Key: MAHOUT-1545
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1545
>             Project: Mahout
>          Issue Type: Bug
>          Components: Classification, CLI, Examples
>    Affects Versions: 0.9
>            Reporter: Andrew Palumbo
>
> The current method for vectorizing data using seq2sparse and then "split" allows for a large amount of information to spill over from the training sets to the test sets- especially in the case of TF-IDF transformations.  The IDF transform provides alot of information on the holdout set to the training set if calculated previous to splitting them up.  
> I'm not sure if given the current seq2sparse implementation's status as Legacy and the relatively minor advantages that it might give whether or not its worth adding something like a "split" option to SparseVectorsFromSequenceFiles.java.  But i know that i saw a new implementation being discussed and and think that it would be worth it to have an option like this built in.    
> I think that this issue may have been raised before, but i wanted to bring it up again in light of the current move away from MapReduce and the new implementations of Mahout tools that will be coming along. 



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