thank you, what a nice compact solution with ave()
I learned something new about the subtleties of R
let me here summarize the alternative solutions, just in case someonelse might
be interested...
thanks, bye
#
# my user function (an example)
mynorm <- function(x) {(x - min(x, na.rm=TRUE))/(max(x, na.rm=TRUE) - min(x,
na.rm=TRUE))}
# my dataframe to apply the formula by blocks
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))
# blocks (factors) to be used for splitting
b <- mydf$blocks
# 1 - split-lapply-unsplit with anonimous function to return a new df
s <- split(mydf, b)
l<- lapply(s, function(x) data.frame(x, v1mod=mynorm(x$v1)))
mydf_new <- unsplit(l, mydf$blocks)
# 2 - split-lapply-unsplit with function trasnform to return a new df
l <- split(mydf, b)
l <- lapply(l, transform, v1.mod = mynorm(v1))
mydf_new <- unsplit(l, b)
# 3 - ave() encapsulating split-lapply-unsplit approach
mydf_new<-transform(mydf, v1.mod = ave(v1, blocks, FUN=mynorm))
#
Da: "William Dunlap" <wdun...@tibco.com>
A: "Massimo Bressan" <massimo.bres...@arpa.veneto.it>
Cc: "David L Carlson" <dcarl...@tamu.edu>, "r-help" <r-help@r-project.org>
Inviato: Venerdì, 13 maggio 2016 19:22:21
Oggetto: Re: [R] apply formula over columns by subset of rows in a dataframe
(to get a new dataframe)
ave() encapsulates the split/lapply/unsplit stuff so
transform(mydf, v1.mod = ave(v1, blocks, FUN=mynorm))
also gives what you got above.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Fri, May 13, 2016 at 7:44 AM, Massimo Bressan <
massimo.bres...@arpa.veneto.it > wrote:
yes, thanks
you pointed me in the right direction: split/unplist was the trick
I completely left behind that possibility!
here the final version
############
mynorm <- function(x) {(x - min(x, na.rm=TRUE))/(max(x, na.rm=TRUE) - min(x,
na.rm=TRUE))}
mydf<-data.frame(blocks=rep(c("a","b","c"),each=5),
v1=round(runif(15,10,25),0), v2=round(rnorm(15,30,5),0))
g <- mydf$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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--
------------------------------------------------------------
Massimo Bressan
ARPAV
Agenzia Regionale per la Prevenzione e
Protezione Ambientale del Veneto
Dipartimento Provinciale di Treviso
Via Santa Barbara, 5/a
31100 Treviso, Italy
tel: +39 0422 558545
fax: +39 0422 558516
e-mail: massimo.bres...@arpa.veneto.it
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