Hi Sean, I'm referring to the paper (http://yifanhu.net/PUB/cf.pdf) Section 2: " However, with implicit feedback it would be natural to assign values to all rui variables. If no action was observed rui is set to zero, thus meaning in our examples zero watching time, or zero purchases on record."
In the implicit setting, apparently there should have values for all pairs (u, i) instead of just the observed ones according to the paper. This is also true for other implicit feedback papers I read. In section 4, when r=0, p=0 BUT c=1. Therefore, when we optimize the value for this pair. (x^Ty)^2 + regularization. Do I misunderstand the paper? Best Regards, Jerry On Mon, Dec 5, 2016 at 2:43 PM, Sean Owen <so...@cloudera.com> wrote: > What are you referring to in what paper? implicit input would never > materialize 0s for missing values. > > On Tue, Dec 6, 2016 at 3:42 AM Jerry Lam <chiling...@gmail.com> wrote: > >> Hello spark users and developers, >> >> I read the paper from Yahoo about CF with implicit feedback and other >> papers using implicit feedbacks. Their implementation require to set the >> missing rating with 0. That is for unobserved ratings, the confidence for >> those is set to 1 (c=1). Therefore, the matrix to be factorized is a dense >> matrix. >> >> I read the source code of the ALS implementation in spark (version 1.6.x) >> for implicit feedback. Apparently, it ignores rating that is 0 (Line 1159 >> in ALS.scala). It could be a mistake or it could be an optimization. Just >> want to see if anyone steps on this yet. >> >> Best Regards, >> >> Jerry >> >
