[R] apply formula over columns by subset of rows in a dataframe (to get a new dataframe)

[William Dunlap]

ave() encapsulates the split/lapply/unsplit stuff so
   transform(mydf, v1.mod = ave(v1, blocks, FUN=mynorm))
also gives what you got above.

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Fri, May 13, 2016 at 7:44 AM, Massimo Bressan <
massimo.bressan at arpa.veneto.it> wrote:

> yes, thanks
>
> you pointed me in the right direction: split/unplist was the trick
>
> I completely left behind that possibility!
>
> here the final version
>
> ############
>
> mynorm <- function(x) {(x - min(x, na.rm=TRUE))/(max(x, na.rm=TRUE) -
> min(x, na.rm=TRUE))}
>
> mydf<-data.frame(blocks=rep(c("a","b","c"),each=5),
> v1=round(runif(15,10,25),0), v2=round(rnorm(15,30,5),0))
>
> g <- mydf$blocks
> l <- split(mydf, g)
> l <- lapply(l, transform, v1.mod = mynorm(v1))
> mydf_new <- unsplit(l, g)
>
> ############
>
> thanks again
>
> massimo
>
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