
Hi dear R list members,
I am trying to create a numerical variable that tracks the visits/entries that a subject has had. For example having a database of repeated serial measurements that are ordered by subject and time. So I would get a variable that says 0 for baseline visit/measurement, 1 for the second etc.
In my case the unique identifier for each subject is AreaID
Will the following code I can number the visits as long as I create as many lines as visits.
But there is probably a way of coding a function or maybe there is already a function.
DUP<-rep(0,length(AreaID))DUP[2:length(DUP)]<-sapply(2:(length(AreaID),function(x) ifelse(AreaID[x]==AreaID[x-1],1,DUP[x]))DUP[3:length(DUP)]<-sapply(3:(
length(AreaID),function(x) ifelse(AreaID[x]==AreaID[x-2],2,DUP[x]))
My Guess was:
AddLag<-function(x) {		DUP<-c(rep(0,length(x)))	for (i in 1:(max(as.numeric(GraphArtDB$Measure))+2)){			DUP[(i+1):length(x)]<-sapply(((i+1):length(x)),function(x) ifelse(x[i]==x[x-i],i,DUP[x]))	}		return(DUP)		}

But it didn´t work.
Any suggestions?

Thanks in advance

J ToledoUPennUSA 		 	   		  
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