How about this? > indx <- unique(cbind(Dates, Groups)) > indx Dates Groups [1,] "12/10/2010" "A" [2,] "12/10/2010" "B" [3,] "13/10/2010" "A" [4,] "13/10/2010" "B" [5,] "13/10/2010" "C"
> indx <- data.frame(indx, id=1:nrow(indx)) > indx Dates Groups id 1 12/10/2010 A 1 2 12/10/2010 B 2 3 13/10/2010 A 3 4 13/10/2010 B 4 5 13/10/2010 C 5 > newdata <- merge(data, indx) > newdata Dates Groups id 1 12/10/2010 A 1 2 12/10/2010 B 2 3 12/10/2010 B 2 4 13/10/2010 A 3 5 13/10/2010 B 4 6 13/10/2010 C 5 ---------------------------------------------- David L Carlson Associate Professor of Anthropology Texas A&M University College Station, TX 77843-4352 -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Chandra Salgado Kent Sent: Tuesday, August 02, 2011 2:12 AM To: r-help@r-project.org Subject: [R] Loops to assign a unique ID to a column Dear R help, I am fairly new in data management and programming in R, and am trying to write what is probably a simple loop, but am not having any luck. I have a dataframe with something like the following (but much bigger): Dates<-c("12/10/2010","12/10/2010","12/10/2010","13/10/2010", "13/10/2010", "13/10/2010") Groups<-c("A","B","B","A","B","C") data<-data.frame(Dates, Groups) I would like to create a new column in the dataframe, and give each distinct date by group a unique identifying number starting with 1, so that the resulting column would look something like: ID<-c(1,2,2,3,4,5) The loop that I have started to write is something like this (but doesn't work!): data$ID<-as.number(c()) for(i in unique(data$Dates)){ for(j in unique(data$Groups)){ data$ID[i,j]<-i i<-i+1 } } Am I on the right track? Any help on this is much appreciated! Chandra [[alternative HTML version deleted]] ______________________________________________ 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.