[jira] Commented: (MAHOUT-391) Make vector more space efficient with variable-length encoding, et al

["Robin Anil (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12864292#action_12864292 ] 

Robin Anil commented on MAHOUT-391:
-----------------------------------

I am getting build errors. Maybe you are different JUnit version ?

/Users/robinanil/mahout/core/src/test/java/org/apache/mahout/math/VarintTest.java:[65,6] cannot find symbol
symbol  : method assertEquals(long,long)
location: class org.apache.mahout.math.VarintTest


> Make vector more space efficient with variable-length encoding, et al
> ---------------------------------------------------------------------
>
>                 Key: MAHOUT-391
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-391
>             Project: Mahout
>          Issue Type: Improvement
>    Affects Versions: 0.3
>            Reporter: Sean Owen
>            Assignee: Sean Owen
>            Priority: Minor
>             Fix For: 0.4
>
>         Attachments: MAHOUT-391.patch
>
>
> There are a few things we can do to make Vector representations smaller on disk:
> - Use variable-length encoding for integer values like size and element indices in sparse representations
> - Further, delta-encode indices in sequential representations
> - Let caller specify that precision isn't crucial in values, allowing it to store values as floats
> Since indices are usually small-ish, I'd guess this saves 2 bytes or so on average, out of 12 bytes per element now.
> Using floats where applicable saves another 4. Not bad.

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