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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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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