Hi, Try: dat1<- read.table(text=" ID Date x2 x1 x3 56 25-Jun-01 10 2 126 56 29-Oct-01 10 2 140 56 18-Mar-02 10 2 445 56 6-Jun-03 10 2 224 56 16-Jan-04 10 2 NA 58 10-Jan-02 10.8 1 715 58 26-Dec-03 10.8 1 NA ",sep="",header=TRUE,stringsAsFactors=FALSE) unlist(with(dat1,by(as.Date(Date,format="%d-%b-%y"),ID,FUN=function(x) c(diff(x),NA))),use.names=FALSE) #[1] 126 140 445 224 NA 715 NA #or unlist(lapply(split(dat1,dat1$ID),function(x) c(diff(as.Date(x$Date,format="%d-%b-%y")),NA)),use.names=FALSE) #[1] 126 140 445 224 NA 715 NA A.K.
________________________________ From: farnoosh sheikhi <farnoosh...@yahoo.com> To: "smartpink...@yahoo.com" <smartpink...@yahoo.com> Sent: Tuesday, July 23, 2013 3:11 PM Subject: subtracting rows for unique Hi there, Hope you are doing well. I have a data set which looks like below, I want to create a new variable (x3-here) which subtracts the date for unique ID. For example for ID 56, the first value is the difference between 29-Oct, and 25-June. Thanks for your help and time. ID Date x2 x1 x3 56 25-Jun-01 10 2 126 56 29-Oct-01 10 2 140 56 18-Mar-02 10 2 445 56 6-Jun-03 10 2 224 56 16-Jan-04 NA NA 58 10-Jan-02 10.8 1 715 58 26-Dec-03 10.8 1 NA Best,Farnoosh Sheikhi ______________________________________________ R-help@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.
