Hi Amit, You are right, the non-corated items are not filtered out in the distributed implementation.
--sebastian On 26.11.2013 20:51, Amit Nithian wrote: > Hi all, > > Apologies if this is a repeat question as I just joined the list but I have > a question about the way that metrics like Cosine and Pearson are > calculated in Hadoop "mode" (i.e. non Taste). > > As far as I understand, the vectors used for computing pairwise item > similarity in Taste are based on the co-rated items; however, in the Hadoop > implementation, I don't see this done. > > The implementation of the distributed item-item similarity comes from this > paper http://ssc.io/wp-content/uploads/2012/06/rec11-schelter.pdf. I didn't > see anything in this paper about filtering out those elements from the > vectors not co-rated and this can make a difference especially when you > normalize the ratings by dividing by the average item rating. In some > cases, the # users to divide by can be fewer depending on the sparseness of > the vector. > > Any clarity on this would be helpful. > > Thanks! > Amit >
