Unless X has 17,770*480,189 elements like the netflix dataset. Then you can use something like this: <a href="http://sifter.org/~simon/journal/20061211.html" rel="nofollow">http://sifter.org/~simon/journal/20061211.html</a><p>The site is currently down, google chache link: <a href="http://209.85.129.132/search?q=cache:h4Ljyun3gUcJ:sifter.org/~simon/journal/20061211.html+simon+funk+try+this+at+home" rel="nofollow">http://209.85.129.132/search?q=cache:h4Ljyun3gUcJ:sifter.org...</a>