Monthly Archives: April 2008

speed issue in R computing: apply() vs a loop

April 23, 2008
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In R, apply() is NOT faster than a loop!!I don't know where I pick up this perception about apply() being faster than a loop in R. For a long time, I always think that apply() runs a function (for example, mean()) on a data structure (row or column) i...

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An R Wiki

April 21, 2008
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An R Wiki

It’s been ages since I visited the R website, so I don’t know how long they’ve had a wiki. It’s built using DokuWiki, one of my personal favourites. This is a great leap forward for R documentation, which is somewhat notorious for being (a) difficult to find and (b) difficult to understand when you find

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The CDK/Metabolomics/Chemometrics Unconference results

April 7, 2008
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The CDK/Metabolomics/Chemometrics Unconference results

As announced earlier, Miguel, Velitchka, Christoph and I held a small CDK/Metabolomics/Chemometrics unconference. We started late, and did not have an evening program, resulting in not overly much results. However, we did do molecular chemometrics.We u...

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Heteroscedasticity

April 6, 2008
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If a model is estimated using the following code: lm(y~x1+x2)-__p 1. bptest(p) does the Breuch Pagan test to formally check presence of heteroscedasticity. To use bptest, you will have to call lmtest library. 2. If the test is positive (low p value), you should see if any transformation of the dependent variable helps you eliminate

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