That doesn't mean this 0 value is literally included in the input. There's no need for that.
On Tue, Dec 6, 2016 at 4:24 AM Jerry Lam <chiling...@gmail.com> wrote: > 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 > > >
