[R] Sorting and subsetting

[Joshua Wiley]

On Mon, Sep 20, 2010 at 10:27 AM, Phil Spector
<spector at stat.berkeley.edu> wrote:
> Harold -
>   Two ways that come to mind:
>
> 1) do.call(rbind,lapply(split(tmp,tmp$index),function(x)x[1:5,]))
> 2) subset(tmp,unlist(tapply(foo,index,seq))<=5)
3) do.call(rbind, by(tmp, tmp$index, .Primitive("["), 1:5, 1:2))

Josh

>
>                                        - Phil Spector
>                                         Statistical Computing Facility
>                                         Department of Statistics
>                                         UC Berkeley
>                                         spector at stat.berkeley.edu
>
>
>
> On Mon, 20 Sep 2010, Doran, Harold wrote:
>
>> Suppose I have a data frame, such as the one below:
>>
>> tmp <- data.frame(index = gl(2,20), foo = rnorm(40))
>>
>> And further assume it is sorted by index and then by the variable foo.
>>
>> tmp <- tmp[order(tmp$index, tmp$foo) , ]
>>
>> Now, I want to grab the first N rows of tmp for each index. In the end,
>> what I want is the data frame 'result'
>>
>> tmp1 <- subset(tmp, index == 1)
>> tmp2 <- subset(tmp, index == 2)
>>
>> tmp1 <- tmp1[1:5,]
>> tmp2 <- tmp2[1:5,]
>> result <- rbind(tmp1, tmp2)
>>
>> Does anyone see a way to subset and subsequently bind without a loop?
>>
>> Harold
>>
>>
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> 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.
>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/