This might be a bug... R^2 should always be in [0,1] and variance should
never be negative.
Can you give more details on which version of Spark you are running?
On Sun, Jul 12, 2015 at 8:37 AM, Sean Owen <so...@cloudera.com> wrote:
> In general, R2 means the line that was fit is a very poor fit -- the
> mean would give a smaller squared error. But it can also mean you are
> applying R2 where it doesn't apply. Here, you're not performing a
> linear regression; why are you using R2?
>
> On Sun, Jul 12, 2015 at 4:22 PM, afarahat <ayman.fara...@yahoo.com> wrote:
> > Hello;
> > I am using the ALS recommendation MLLibb. To select the optimal rank, I
> have
> > a number of users who used multiple items as my test. I then get the
> > prediction on these users and compare it to the observed. I use
> > the RegressionMetrics to estimate the R^2.
> > I keep getting a negative value.
> > r2 = -1.18966999676 explained var = -1.18955347415 count = 11620309
> > Here is my Pyspark code :
> >
> > train1.cache()
> > test1.cache()
> >
> > numIterations =10
> > for i in range(10) :
> > rank = int(40+i*10)
> > als = ALS(rank=rank, maxIter=numIterations,implicitPrefs=False)
> > model = als.fit(train1)
> > predobs =
> > model.transform(test1).select("prediction","rating").map(lambda p :
> > (p.prediction,p.rating)).filter(lambda p: (math.isnan(p[0]) == False))
> > metrics = RegressionMetrics(predobs)
> > mycount = predobs.count()
> > myr2 = metrics.r2
> > myvar = metrics.explainedVariance
> > print "hooo",rank, " r2 = ",myr2, "explained var = ", myvar,
> "count
> > = ",mycount
> >
> >
> >
> >
> > --
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