Many thanks,
truly a simple and elegant solution!
Caroline
On Sun, Sep 13, 2009 at 12:08 AM, David Winsemius
<dwinsem...@comcast.net> wrote:
>
> 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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