I think as.numeric(! duplicated(group)) might do this for you ...
On Sat, Nov 30, 2024, 9:27 PM Sorkin, John <jsor...@som.umaryland.edu>
wrote:
> Dear R help folks,
>
> First my apologizes for sending several related questions to the list
> server. I am trying to learn how to manipulate data in R . . . and am
> having difficulty getting my program to work. I greatly appreciate the help
> and support list member give!
>
> I am trying to write a program that will run through a data frame
> organized by ID and for the first line of each new group of data lines that
> has the same ID create a new variable first that will be 1 for the first
> line of the group and 0 for all other lines.
>
> e.g. if my original data is
> olddata
> ID date
> 1 1
> 1 1
> 1 2
> 1 2
> 1 3
> 1 3
> 1 4
> 1 4
> 1 5
> 1 5
> 2 5
> 2 5
> 2 5
> 2 6
> 2 6
> 2 6
> 3 10
> 3 10
>
> the new data will be
> newdata
> ID date first
> 1 1 1
> 1 1 0
> 1 2 0
> 1 2 0
> 1 3 0
> 1 3 0
> 1 4 0
> 1 4 0
> 1 5 0
> 1 5 0
> 2 5 1
> 2 5 0
> 2 5 0
> 2 6 0
> 2 6 0
> 2 6 0
> 3 10 1
> 3 10 0
>
> When I run the program below, I receive the following error:
> Error in df[, "ID"] : incorrect number of dimensions
>
> My code:
> # Create data.frame
> ID <- c(rep(1,10),rep(2,6),rep(3,2))
> date <- c(rep(1,2),rep(2,2),rep(3,2),rep(4,2),rep(5,2),
> rep(5,3),rep(6,3),rep(10,2))
> olddata <- data.frame(ID=ID,date=date)
> class(olddata)
> cat("This is the original data frame","\n")
> print(olddata)
>
> # This function is supposed to identify the first row
> # within each level of ID and, for the first row, set
> # the variable first to 1, and for all rows other than
> # the first row set first to 0.
> mydoit <- function(df){
> value <- ifelse (first(df[,"ID"]),1,0)
> cat("value=",value,"\n")
> df[,"first"] <- value
> }
> newdata <- aggregate(olddata,list(olddata[,"ID"]),mydoit)
>
> Thank you,
> John
>
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine, University of Maryland School of Medicine;
> Associate Director for Biostatistics and Informatics, Baltimore VA Medical
> Center Geriatrics Research, Education, and Clinical Center;
> PI Biostatistics and Informatics Core, University of Maryland School of
> Medicine Claude D. Pepper Older Americans Independence Center;
> Senior Statistician University of Maryland Center for Vascular Research;
>
> Division of Gerontology and Paliative Care,
> 10 North Greene Street
> <https://www.google.com/maps/search/10+North+Greene+Street?entry=gmail&source=g>
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> Cell phone 443-418-5382
>
>
>
> ______________________________________________
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