[R] apply function across two variables by mult factors

[Gabor Grothendieck]

Try this:

transform(testDF, value = as.numeric(paste(round(abs(x)),
round(abs(y)), sep = ".")))


On Wed, Sep 16, 2009 at 3:22 PM, Jon Loehrke <jloehrke at umassd.edu> wrote:
> Greetings,
>
> I am attempting to run a function, which produces a vector and
> requires two input variables, across two nested factor levels.  I can
> do this using by(X, list(factor1, factor2), function), however I
> haven't found a simple way to extract the list output into an
> organized vector form.  I can do this using nested loops but it isn't
> exactly an optimal approach.
>
> Thank you for any and all suggestions.  Jon
>
> # example data frame
> testDF<-data.frame(
>        x=rnorm(12),
>        y=rnorm(12),
>        f1=gl(3,4),
>        f2=gl(2,2,12))
>
> # example function [trivial]
> testFun<-function(x){
>        X<-abs(x[,1]);
>        Y<-abs(x[,2]);
>        as.numeric(     paste(round(X), round(Y), sep='.'))
>        }
>
> # apply by factor levels but hard to extract values
> by(testDF[,1:2], list(testDF$f1, testDF$f2), testFun)
>
> # Loop works, but not efficient for large datasets
> testDF$value<-NA
> for(i in levels(testDF$f1)){
>        for(j in levels(testDF$f2)){
>                testDF[testDF$f1==i & testDF$f2==j,]$value<-testFun(testDF[testDF
> $f1==i & testDF$f2==j,1:2])
>                }
>        }
> testDF
> sessionInfo()
> #R version 2.9.1 Patched (2009-08-07 r49093)
> #i386-apple-darwin8.11.1
> #
> #locale:
> #en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
> #
> #attached base packages:
> #[1] stats     graphics  grDevices utils     datasets  methods   base
>
>
> Jon Loehrke
> Graduate Research Assistant
> Department of Fisheries Oceanography
> School for Marine Science and Technology
> University of Massachusetts
> 200 Mill Road, Suite 325
> Fairhaven, MA 02719
> jloehrke at umassd.edu
> T 508-910-6393
> F 508-910-6396
>
>
>        [[alternative HTML version deleted]]
>
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