You can do this with split/unsplit: > mydf.split <- split(mydf, mydf$blocks) > str(mydf.split) List of 3 $ a:'data.frame': 5 obs. of 3 variables: ..$ blocks: Factor w/ 3 levels "a","b","c": 1 1 1 1 1 ..$ v1 : num [1:5] 19 15 17 22 16 ..$ v2 : num [1:5] 35 31 35 31 39 $ b:'data.frame': 5 obs. of 3 variables: ..$ blocks: Factor w/ 3 levels "a","b","c": 2 2 2 2 2 ..$ v1 : num [1:5] 12 24 25 22 18 ..$ v2 : num [1:5] 31 19 35 32 38 $ c:'data.frame': 5 obs. of 3 variables: ..$ blocks: Factor w/ 3 levels "a","b","c": 3 3 3 3 3 ..$ v1 : num [1:5] 17 14 21 21 22 ..$ v2 : num [1:5] 27 25 23 23 27 > mydf.split2 <- lapply(mydf.split, function(x) data.frame(x, + v1mod=mynorm(x$v1))) > str(mydf.split2) List of 3 $ a:'data.frame': 5 obs. of 4 variables: ..$ blocks: Factor w/ 3 levels "a","b","c": 1 1 1 1 1 ..$ v1 : num [1:5] 19 15 17 22 16 ..$ v2 : num [1:5] 35 31 35 31 39 ..$ v1mod : num [1:5] 0.571 0 0.286 1 0.143 $ b:'data.frame': 5 obs. of 4 variables: ..$ blocks: Factor w/ 3 levels "a","b","c": 2 2 2 2 2 ..$ v1 : num [1:5] 12 24 25 22 18 ..$ v2 : num [1:5] 31 19 35 32 38 ..$ v1mod : num [1:5] 0 0.923 1 0.769 0.462 $ c:'data.frame': 5 obs. of 4 variables: ..$ blocks: Factor w/ 3 levels "a","b","c": 3 3 3 3 3 ..$ v1 : num [1:5] 17 14 21 21 22 ..$ v2 : num [1:5] 27 25 23 23 27 ..$ v1mod : num [1:5] 0.375 0 0.875 0.875 1 > mydf2 <- unsplit(mydf.split2, mydf$blocks) > str(mydf2) 'data.frame': 15 obs. of 4 variables: $ blocks: Factor w/ 3 levels "a","b","c": 1 1 1 1 1 2 2 2 2 2 ... $ v1 : num 19 15 17 22 16 12 24 25 22 18 ... $ v2 : num 35 31 35 31 39 31 19 35 32 38 ... $ v1mod : num 0.571 0 0.286 1 0.143 ...
------------------------------------- David L Carlson Department of Anthropology Texas A&M University College Station, TX 77840-4352 -----Original Message----- From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Massimo Bressan Sent: Friday, May 13, 2016 6:56 AM To: r-help@r-project.org Subject: [R] apply formula over columns by subset of rows in a dataframe (to get a new dataframe) hi I need to apply a user defined formula over some selected columns of a dataframe by subsetting group of rows (blocks) and get back a new dataframe I’ve been managed to get the the calculations right but I’m not satisfied at all by the form of the results please refer to my reproducible example ########## # 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)) #my attempts (not satisfied by final output) tapply(mydf$v1, mydf$blocks, mynorm) byf<-factor(mydf$blocks) aggregate(mydf[2:3], list(byf), mynorm) aggregate(mydf[2:3], list(mydf$blocks), mynorm, simplify = FALSE) ########### please can anyone give me some hints on how to properly proceed? I need a dataframe with all variables as final result sorry but I’m sort of definitely stuck with this… thanks [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
