[R] selection by two unique variables

[jim holtman]

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.