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From "Mugoma Joseph Okomba" <mug...@yengas.com>
Subject Re: Exclusing certain ratings when running recommender
Date Wed, 09 May 2012 08:08:26 GMT

>From javadoc
(https://builds.apache.org/job/Mahout-Quality/javadoc/org/apache/mahout/cf/taste/impl/recommender/GenericUserBasedRecommender.html#recommend(long,%20int,%20org.apache.mahout.cf.taste.recommender.IDRescorer)

rescorer - rescoring function to apply before final list of
recommendations is determined

My take is that IDRescorer is used to determine the final list of
recommendations (via filtering or re-scoring) but doesn't apply on the
original items.

To be clear let me give small demonstration:
1. Item 1 => rating 3
2. Item 2 => rating 2
3. Item 3 => rating 1
4. Item 4 => rating 3
5. Item 5 => rating 2
6. Item 6 => rating 4
7. Item 7 => rating 2
8. Item 8 => rating 3
9. Item 9 => rating 4
10. Item 10 => rating 4

Original items => 10

What IDRescorer does is compute recommendations then exclude items 6,9 &
10 from final list via filtering.

What I need is that, before recommendations are computed, only items
1,2,3,4,5,7,8 are considered i.e. original items should be reduced from 10
to 7 and only the 7 items should be considered by the recommender.


On Wed, May 9, 2012 10:18 am, Sean Owen wrote:
> Filtering happens on "original items" if I understand you correctly.
> Conceptually, it goes like...
>
>
>    1. Candidate items are chosen
>    2. (Optionally) Items are filtered
>    3. Items are scored
>    4. (Optionally) Items are rescored
>    5. The top K are returned
>
>
> On Wed, May 9, 2012 at 7:21 AM, Mugoma Joseph Okomba
> <mugoma@yengas.com>wrote:
>
>> On Wed, May 9, 2012 7:37 am, Sean Owen wrote:
>> > Actually that's how IDRescorer already works. It will filter before
>> > scoring.
>> >
>>
>> Does 'before scoring' mean before the recommender extracts
>> recommendations?
>>
>> The way I have used IDRescorer before is as a way of filtering out
>> recommendations I didn't want to be seen. I assumed that the filtering
>> happens on the recommended items, not on the original items. Am I wrong
>> on
>> this?
>>
>> Thanks.
>>
>> Mugoma.
>>
>>
>



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