[R] different results form summarization by loop and sum or rowMeans function

[jim holtman]

How low is "very low"?  This is probably answered by FAQ 7.31

On Thu, Sep 11, 2008 at 9:49 AM, Markus Schmidberger
<schmidb at ibe.med.uni-muenchen.de> wrote:
> Hi,
>
> I found different results calculating the rowMeans by the function
> rowMeans() and a simple for-loop. The differences are very low. But after
> this calculation I will start some optimization algorithms (BFGS or CG) and
> there I get huge differences (from the small changes in the beginning or
> start values, I changed nothing else in the code).
> How I can avoid these differences between sum-loops and sum-functions?
>
> Attached a small testcode using data form Bioconductor.
>
> Best
> Markus
>
>
> library(affy)
> data(affybatch.example)
> mat <- exprs(affybatch.example)[1:100,1:3]
> mat <- exp(1)*mat
> mat <- asinh(mat)
>
> rowM1<- rowMeans(mat)
>
> t=rep(0,100) # Vektor mit 0en
> for(i in 1:100){
>  for(j in 1:3)
>      t[i] <- t[i] + mat[i,j]
> }
> rowM2 <- t/3
>
> m1 <- mat - rowM1
> m2 <- mat -rowM2
>
> print(m1-m2)
>
> sessionInfo()
> R version 2.7.1 (2008-06-23)
> i386-pc-mingw32
>
> locale:
> LC_COLLATE=German_Germany.1252;LC_CTYPE=German_Germany.1252;LC_MONETARY=German_Germany.1252;LC_NUMERIC=C;LC_TIME=German_Germany.1252
>
> attached base packages:
> [1] tools     stats     graphics  grDevices utils     datasets  methods [8]
> base
> other attached packages:
> [1] affy_1.18.2          preprocessCore_1.2.0 affyio_1.8.0       [4]
> Biobase_2.0.1
> --
> Dipl.-Tech. Math. Markus Schmidberger
>
> Ludwig-Maximilians-Universität München
> IBE - Institut für medizinische Informationsverarbeitung,
> Biometrie und Epidemiologie
> Marchioninistr. 15, D-81377 Muenchen
> URL: http://ibe.web.med.uni-muenchen.de Mail: Markus.Schmidberger [at]
> ibe.med.uni-muenchen.de
> Tel: +49 (089) 7095 - 4599
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?