getAllOtherItems

[Tamas Jambor <ja...@gmail.com>]

hi,

I have just spotted a possible bug in AbstractRecommender, the 
getAllOtherItems only gets items if there is at least one co-rated item 
between the target user and other users. For example if there are only 
two users in the system and they didn't co-rate any items than this 
method returns nothing.

Tamas

Re: getAllOtherItems

[Ted Dunning <te...@gmail.com>]

This is definitely true and in a few very sparse problems, these might even
be usable recommendations.

In general, having some cooccurrence is a useful heuristic.  If you find it
useful, you can replace the candidate strategy.

A good example of an SVD-like algorithm that could produce strong
recommendations with no-cooccurrence, see here:
http://arxiv.org/abs/1006.2156

We don't much support side information in Mahout so this the candidate set
problem associated with these models isn't an issue yet, but at some point
using these models might be good.  The primary benefit would be better
performance in cold-start situations.

On Sun, Aug 15, 2010 at 11:18 AM, Tamas Jambor <ja...@gmail.com> wrote:

> On 15/08/2010 18:29, Sebastian Schelter wrote:
>
>> What talk about is actually not a bug, if there are no co-rated items
>> it's absolutely logical that nothing can be recommended. In a real world
>> application you would maybe want to show the user the latest or overall
>> top-rated items as a workaround (just to show them something).
>>
>>
>
> Thanks, it's true for neighbourhood based algorithms, but SVD could still
> give you results.
>
> Tamas
>

Re: getAllOtherItems

[Sean Owen <sr...@gmail.com>]

(True, the SVD's real benefit is that it can build more user-user
and/or item-item connections by squeezing the data down into many
fewer dimensions. It's making more items be co-rated in a sense.)

On Sun, Aug 15, 2010 at 1:18 PM, Tamas Jambor <ja...@gmail.com> wrote:
> On 15/08/2010 18:29, Sebastian Schelter wrote:
>>
>> What talk about is actually not a bug, if there are no co-rated items
>> it's absolutely logical that nothing can be recommended. In a real world
>> application you would maybe want to show the user the latest or overall
>> top-rated items as a workaround (just to show them something).
>>
>
> Thanks, it's true for neighbourhood based algorithms, but SVD could still
> give you results.
>
> Tamas
>

Re: getAllOtherItems

[Tamas Jambor <ja...@gmail.com>]

On 15/08/2010 18:29, Sebastian Schelter wrote:
> What talk about is actually not a bug, if there are no co-rated items
> it's absolutely logical that nothing can be recommended. In a real world
> application you would maybe want to show the user the latest or overall
> top-rated items as a workaround (just to show them something).
>    

Thanks, it's true for neighbourhood based algorithms, but SVD could 
still give you results.

Tamas

Re: getAllOtherItems

[Sebastian Schelter <ss...@apache.org>]

Hi Tamas,

are you looking at the current trunk of Mahout 0.4? We made the method
use a customizable "CandidateItemsStrategy" implementation lately. I
guess you're talking about
PreferredItemsNeighborhoodCandidateItemsStrategy then which is the
default implementation.

What talk about is actually not a bug, if there are no co-rated items
it's absolutely logical that nothing can be recommended. In a real world
application you would maybe want to show the user the latest or overall
top-rated items as a workaround (just to show them something).

--sebastian

Am 15.08.2010 19:22, schrieb Tamas Jambor:
> hi,
>
> I have just spotted a possible bug in AbstractRecommender, the
> getAllOtherItems only gets items if there is at least one co-rated
> item between the target user and other users. For example if there are
> only two users in the system and they didn't co-rate any items than
> this method returns nothing.
>
> Tamas

Re: getAllOtherItems

[Grant Ingersoll <gs...@apache.org>]

From http://people.apache.org/~hossman/#threadhijack

When starting a new discussion on a mailing list, please do not reply to 
an existing message, instead start a fresh email.  Even if you change the 
subject line of your email, other mail headers still track which thread 
you replied to and your question is "hidden" in that thread and gets less 
attention.   It makes following discussions in the mailing list archives 
particularly difficult.

See Also:  
http://en.wikipedia.org/wiki/User:DonDiego/Thread_hijacking


On Aug 15, 2010, at 1:22 PM, Tamas Jambor wrote:

> hi,
> 
> I have just spotted a possible bug in AbstractRecommender, the getAllOtherItems only gets items if there is at least one co-rated item between the target user and other users. For example if there are only two users in the system and they didn't co-rate any items than this method returns nothing.
> 
> Tamas