try this:
> x <- read.table(text = "id wtdt wt
lastpk
+
+ 64050256 2010-09-18 275 2010-09-16
+
+ 64050256 2010-09-19 277 2010-09-18
+
+ 64050256 2010-09-20 272 2010-09-18
+
+ 64050256 2010-09-21 277 2010-09-18", as.is = TRUE, header =
TRUE)>
> first <- lapply(split(x, list(x$id, x$lastpk), drop = TRUE),
function(a){
+ a[1,, drop = FALSE]
+ })> do.call(rbind, first)
id wtdt wt lastpk
64050256.2010-09-16 64050256 2010-09-18 275 2010-09-16
64050256.2010-09-18 64050256 2010-09-19 277 2010-09-18>
>
>
On Wed, May 2, 2012 at 11:23 AM, Bert Gunter <gunter.berton at gene.com>
wrote:> ?tapply
>
> ?with is also useful here
>
> as in (untested)
> with(yourdataframe, tapply(lastpk, id, unique))
>
> -- Bert
>
> On Wed, May 2, 2012 at 7:58 AM, Ayyappa Chaturvedula
> <ayyappach at gmail.com> wrote:
>> Dear Group,
>>
>> I am working with a large dataset where I need to select for each
unique id
>> the the unique lastpk row. ?Here is a sample subject:
>>
>> ? ? ? ? ?id ? ? ? ? ? ? wtdt ? ? ? ? ? wt ? ? ? ? lastpk
>>
>> ?64050256 2010-09-18 ? 275 ?2010-09-16
>>
>> ?64050256 2010-09-19 ? 277 ?2010-09-18
>>
>> ?64050256 2010-09-20 ? 272 ?2010-09-18
>>
>> ?64050256 2010-09-21 ? 277 ?2010-09-18
>>
>>
>>
>> I want the result as:
>>
>> ? ? ? id ? ? ? ? ? ? ? wtdt ? ? ? ? wt ? ? ?lastpk
>>
>> 64050256 2010-09-18 275 2010-09-16
>>
>> 64050256 2010-09-19 277 2010-09-18
>>
>>
>>
>> I am using !(duplicated(data$id)) to select the first row but now I
want to
>> select the first row of the unique lastpk in each unique id.
>>
>>
>>
>> I appreciate your help on this.
>>
>>
>>
>> Regards,
>>
>> Ayyappa
>>
>> ? ? ? ?[[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at 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.
>
>
>
> --
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
>
> Internal Contact Info:
> Phone: 467-7374
> Website:
>
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
>
> ______________________________________________
> R-help at 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.
--
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.