[R] Add sequence numbers to lines with the same ID: How can this be accomplished?

[John Sorkin]

I have a file that has (1) Line numbers, (2) IDs. A given ID number can appear in more than one row. For each row with a repeated ID, I want to add a number that gives the sequence number of the repeated ID number. The R code below demonstrates what I want to have, without any attempt to produce the result, as I have no idea how to accomplish my goal.


line <- c(1,2,3,4,5,6,7,8,9,10)
ID<-    c(1,1,2,3,4,5,6,7,8,8)
cat("Note lines 1 and 2 both contain ID 1; lines 9 and 10 both contain ID 8")
cbind(line,ID)
Seq <-  c(1,2,1,1,1,1,1,1,1,2)
cat("Sequence numbers within ID added to the data")
cbind(line,ID,Seq)



John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
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