On Sep 12, 2009, at 11:36 AM, caroline choong wrote:
Dear all,
I have a data set as follows:
ID cycle.number cycle.result
1 2525 1 38
2 2525 2 38
3 2525 3 25
4 2525 4 25
5 2525 5 25
6 2525 6 25
7 2531 1 38
8 2531 2 38
9 2078 1 38
10 2078 2 38
I want to find out the maximum cycle.number for each ID, and later
find the
corresponding cycle.result for that cycle.
I have already managed to pull out the maximum cycle by using a for
loop:
max.cycle <- vector()
patients <- (levels(factor(ID)))
for (i in 1:length(patients)) {
max.cycle[i] <- max(cycle.number[(ID %in% patients[i] )])
}
But i would like to know if there is a better or more elegant way of
pulling
out the maximum cycle.number for each ID?
There is:
?tapply
> patients <- read.table(textConnection(" ID
cycle.number cycle.result
+ 1 2525 1 38
+ 2 2525 2 38
+ 3 2525 3 25
+ 4 2525 4 25
+ 5 2525 5 25
+ 6 2525 6 25
+ 7 2531 1 38
+ 8 2531 2 38
+ 9 2078 1 38
+ 10 2078 2 38"), header=TRUE)
> tapply(patients$cycle.number, patients$ID, max)
2078 2525 2531
2 6 2
Perhaps without the need for using
a for loop?
Many thanks,
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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