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From charlysf <>
Subject Questions about PearsonCorrelation on a example
Date Tue, 23 Jun 2009 22:38:36 GMT


I use PearsonCorrelation, and I would like to understand why on my example,
I have a NaN. 

I use PearsonCorrelation for an Item Basis recommender, and I of course
expect, to have a similarity between the two items, because they are linked
to a same user.

But in fact, I have a NaN.

I saw that the mean of the data should be 0, but or me, 0 is the neutral
score, and I can't be sure that for each user, their mean is 0, is it
important ? I don't really understand why.

Thank you.
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