On 03/05/2014 01:23 PM, Juan José Ramos wrote:
Thanks for the reply, Sebastian.
I am not sure if that should be implemented in the Abstract base class
though because for
instance PreferredItemsNeighborhoodCandidateItemsStrategy, by definition,
it returns the item not rated by the user and rated by somebody else.
Good point. So we seem to need special implementations.
Back to my last post, I have been playing around with
AllSimilarItemsCandidateItemsStrategy
and AllUnknownItemsCandidateItemsStrategy, and although they both do what I
wanted (recommend items not previously rated by any user), I honestly can't
tell the difference between the two strategies. In my tests the output was
always the same. If the eventual output of the recommender will not include
items already rated by the user as pointed out here (
http://mail-archives.apache.org/mod_mbox/mahout-user/201403.mbox/%3CCABHkCkuv35dbwF%2B9sK88FR3hg7MAcdv0MP10v-5QWEvwmNdY%2BA%40mail.gmail.com%3E),
AllSimilarItemsCandidateItemsStrategy should be equivalent to
AllUnkownItemsCandidateItemsStrategy, shouldn't it?
AllSimilarItems returns all items that are similar to any item that the
user already knows. AllUnknownItems simply returns all items that the
user has not interacted with yet.
These are two different things, although they might overlap in some
scenarios.
Best,
Sebastian
Thanks.
On Wed, Mar 5, 2014 at 10:23 AM, Sebastian Schelter <s...@apache.org> wrote:
Hi Juan,
that is a good catch. CandidateItemsStrategy is the right place to
implement this. Maybe we should simply extend its interface to add a
parameter that says whether to keep or remove the current users items?
We could even do this in the abstract base class then.
--sebastian
On 03/05/2014 10:42 AM, Juan José Ramos wrote:
In case somebody runs into the same situation, the key seems to be in the
CandidateItemStrategy being passed to the constructor
of GenericItemBasedRecommender. Looking into the code, if no
CandidateItemStrategy is specified in the
constructor, PreferredItemsNeighborhoodCandidateItemsStrategy is used and
as the documentation says, the doGetCandidateItems method: "returns all
items that have not been rated by the user and that were preferred by
another user that has preferred at least one item that the current user
has
preferred too".
So, a different CandidateItemStrategy needs to be passed. For this
problem,
it seems to me that AllSimilarItemsCandidateItemsStrategy,
AllUnknownItemsCandidateItemsStrategy are good candidates. Does anybody
know where to find some documentation about the different
CandidateItemStrategy? Based on the name I would say that:
1) AllSimilarItemsCandidateItemsStrategy returns all similar items
regardless of whether they have been already rated by someone or not.
2) AllUnknownItemsCandidateItemsStrategy returns all similar items that
have not been rated by anyone yet.
Does anybody know if it works like that?
Thanks.
On Tue, Mar 4, 2014 at 9:16 AM, Juan José Ramos <jjar...@gmail.com>
wrote:
First thing is thatI know this requirement would not make sense in a CF
Recommender. In my case, I am trying to use Mahout to create something
closer to a Content-Based Recommender.
In particular, I am pre-computing a similarity matrix between all the
documents (items) of my catalogue and using that matrix as the
ItemSimilarity for my Item-Based Recommender.
So, when a user rates a document, how could I make the recommender
outputs
similar documents to that ones the user has already rated even if no
other
user in the system has rated them yet? Is that even possible in the
first
place?
Thanks a lot.
