Try this:
transform(DF, Time = ave(1:nrow(DF), Subject, FUN = function(ix)
if (any(Marker[ix] == 1)) Time - Time[Marker == 1] else Time))
On Fri, Dec 4, 2009 at 5:47 PM, Dennis Fisher <fis...@plessthan.com> wrote:
> Colleagues,
>
> R 2.9.0 on all platforms
>
> I have a dataset that contains three columns of interest: ID's, serial
> elapsed times, and a marker. Representative data:
> Subject Time Marker
> 1 100.5 0
> 1 101 0
> 1 102 1
> 1 103 0
> 1 105 0
>
> For each subject, I would like to find the time associated with MARKER ==
> 1, then replace Time with Time - (Time[Marker == 1])
> The result for this subject would be:
> Subject Time Marker
> 1 -1.5 0
> 1 -1 0
> 1 0 1
> 1 1 0
> 1 3 0
>
> One proviso: some subjects do not have Marker == 1; for these subjects, I
> would like Time to remain unchanged.
>
> At present, I am looping over each subject. The number of subjects is
> large so this process is quite slow. I assume that one of the apply
> functions could speed this markedly but I am not facile with them. Any help
> would be appreciated.
>
> Dennis
>
> Dennis Fisher MD
> P < (The "P Less Than" Company)
> Phone: 1-866-PLessThan (1-866-753-7784)
> Fax: 1-866-PLessThan (1-866-753-7784)
> www.PLessThan.com
>
> ______________________________________________
> 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.
>
[[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.
