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From Ted Dunning <>
Subject Re: adding feature:skip user's non-interested items when generate recommendation for user.
Date Tue, 24 Aug 2010 04:07:36 GMT
Sorry to chime in late, but removing items after recommendation isn't such a
crazy thing to do.

In particular, it is common to remove previously viewed items (for a period
of time).  Likewise, it the user says "don't show this again", it makes
sense to backstop the actual recommendation system with a UI limitation that
does a post-recommendation elimination.

Moreover, this approach has the great benefit that the results are very
predictable.  Exactly the requested/seen items will be eliminated and no
surprising effect on recommendations will occur.

That predictability is exactly the problem, though.  Generally you want a
bit more systemic effect for negative recommendations.  This is a really
sticky area, however, because negative recommendations often impart
information about positive preferences in addition to some level of negative

I used an explicit filter at both Musicmatch and at Veoh.  Both systems
worked well.  Especially at Veoh, there was a lot of additional machinery
required to handle the related problem of anti-flooding.  That was done at
the UI level as well.

On Mon, Aug 23, 2010 at 8:16 PM, Sean Owen <> wrote:

> (Uncanny, I was just minutes before researching Grooveshark for
> unrelated reasons... Good to hear from any company doing
> recommendations and is willing to talk about it. I know of a number
> that can't or won't unfortunately.)
> Yeah, sounds like we're all on the same page. One key point in what I
> think everyone is talking about is that this is not simply removing
> items *after* recommendations are computed. This risks removing most
> or all recommended items. It needs to be done during the process of
> selecting recommendations.
> But beyond that, it's a simple idea and just a question of
> implementation. It's "Rescorer" in the non-Hadoop code, which does
> more than provide a way to remove items but rather generally rearrange
> recommendations according to some logic. I think it's likely easy and
> useful to imitate this with a simple optional Mapper/Reducer phase in
> this nascent "RecommenderJob" pipeline that Sebastian is now helping
> expand into something more configurable and general purpose.
> Sean
> On Mon, Aug 23, 2010 at 8:25 PM, Chris Bates
> <> wrote:
> > Hi all,
> >
> > I'm new to this forum and haven't seen the code you are talking about, so
> > take this with a grain of salt.  The way we handle "banned items" at
> > Grooveshark is to post-process the itemID pairs in Hive.  If a user
> dislikes
> > a recommended song/artist, an item pair is stored in HDFS and then when
> the
> > recs are computed, those banned user-item pairs are taken into account.
> > Here is an example query:
> >
> > SELECT DISTINCT st.uid, st.simuid, IF(b.uid=st.uid,1,0) as banned  FROM
> > streams_u2u st LEFT OUTER JOIN bannedsimusers b ON (b.simuid=st.simuid);
> >
> > That query will print out a 1 or a 0 if the recommended item pair is
> banned
> > or not.  Hive also supports case statements (I think), so you can make a
> > range of "banned-ness" I guess.  Just another solution to the "dislike"
> > problem.
> >
> > Chris

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