HI, I am not sure whether this is what you want. Mydata<-read.table(text=" idxy ix iy country col5 1 1 1 c1 x1 2 1 2 c1 x2 3 1 3 c1 x3 4 2 4 c1 x4 5 2 4 c2 x5 6 2 5 c2 x6 7 3 5 c3 x7 8 3 5 c3 x8 9 3 5 c3 x9 ",sep="",stringsAsFactors=FALSE,header=TRUE) country1<-as.numeric(gsub(".*(\\d+)","\\1",Mydata$country)) Mydata1<-data.frame(ix=abs(diff(c(Mydata$ix[2],Mydata$ix))),iy=abs(diff(c(Mydata$iy[2],Mydata$iy))),country=abs(diff(c(country1[2],country1)))) Mydata2<- Mydata[apply(Mydata1,1,function(x) all(!duplicated(x)|!duplicated(x,fromLast=TRUE))),] Mydata2$border<-1 res<-merge(Mydata,Mydata2,by.x=c("idxy","ix","iy","country","col5"),by.y=c("idxy","ix","iy","country","col5"),all.x=TRUE) res # idxy ix iy country col5 border #1 1 1 1 c1 x1 1 #2 2 1 2 c1 x2 1 #3 3 1 3 c1 x3 1 #4 4 2 4 c1 x4 1 #5 5 2 4 c2 x5 1 #6 6 2 5 c2 x6 1 #7 7 3 5 c3 x7 1 #8 8 3 5 c3 x8 NA #9 9 3 5 c3 x9 NA
----- Original Message ----- From: Andrew Crane-Droesch <andre...@gmail.com> To: r-help@r-project.org Cc: Sent: Saturday, October 20, 2012 3:36 AM Subject: [R] Help with programming a tricky algorithm Hi All, I'm a little stumped by the following problem. I've got a dataset with the following structure: idxy ix iy country (other variables) 1 1 1 c1 x1 2 1 2 c1 x2 3 1 3 c1 x3 . . . . . 3739 55 67 c7 x3739 3740 55 68 c7 x3740 where ix and iy are interger-valued indices of the actual x and y coordinates for the gridded data I want to define a "border" variable that equals 1 if the cell north, east, west, or south of it has a different value of the country variable. So, for the row with idxy = 1, border would equal 1 if there is any idxy with country !=c1 and ix = 2 (or zero) or iy = 2 (or zero). Any thoughts? Thanks! Andrew ______________________________________________ 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. ______________________________________________ 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.