[R] help sub setting data frame

[Ista Zahn]

Hi Sean,
Comment in line below.

On Thu, Oct 22, 2009 at 5:39 PM, Sean MacEachern <sean.maceach at gmail.com> wrote:
> Hi,
>
> I'm running into a problem subsetting a data frame that I have never
> encountered before:
>
>> dim(chkPd)
> [1] 3213    6
>
>> df = head(chkPd)
>> df
>               PN        WB      Sire     Dam   MG SEX
> 601      1001  715349   61710   61702   67    F
> 969  1001_1  511092 616253 615037 168    F
> 986  1002_1  511082 616253 623905 168    F
> 667      1003  715617   61817   61441   67    F
> 1361 1003_1 510711 635246 627321 168    F
> 754       1004 715272   62356   61380  67     F
>
>
>> dfb = chkPd[df$PN,]
>> dfb
>            PN     WB   Sire    Dam  MG  SEX
> 1001    2114_1 510944 616294 614865 168    M
> NA        <NA>     NA   <NA>   <NA>  NA <NA>
> NA.1      <NA>     NA   <NA>   <NA>  NA <NA>
> 1003    1130_1 510950 616294 619694 168    F
> NA.2      <NA>     NA   <NA>   <NA>  NA <NA>
> 1004 2221-SHR2 510952 616294 619694 168    M
>
>
> I'm not sure why I'm getting this behaviour? By sub-setting the
> original data frame by PN I seem to be pulling out row numbers?
> Therefore I am only getting results where PN is less than the
> dimensions of the original data frame and of course nothing where PN
> has _ in the id. I have also tried using subset but haven't had any
> luck with that either.

That is the documented behavior as far as I can tell. See

?"[.data.frame"

Maybe my brain is going soft at the end of a long day, but I can't
tell what you're trying to do. Can you clarify?

-Ista

>
>
>>dfb = subset(chkPd, PN==df$PN)
> Warning message:
> In PN == df$PN :
>  longer object length is not a multiple of shorter object length
>
> I wasn't aware that both the larger data frame had to be a multiple of
> the object you were sub-setting . In any case I would appreciate any
> insight into what I may be doing wrong.
>
> Cheers,
>
> Sean
>
>
>> sessionInfo()
> R version 2.9.1 (2009-06-26)
> i386-apple-darwin8.11.1
>
> locale:
> en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
>
> attached base packages:
> [1] splines   stats     graphics  grDevices utils     datasets  methods   base
>
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org