[R] help sub setting data frame

[Sean MacEachern]

Hi Ista,

I think I'm suffering long dayitis myself. You are probably right. I
don't use subset that often. I typically use brackets to subset
dataframes. Essentially what I am trying to do is take my original
dataframe (chkPd) and subset it using a smaller dataframe with some
matching PN IDs. They are only a few hundred rows different in size so
subset wouldn't be appropriate here. I'm just struggling to figure out
what's going wrong in my first example.
for instance if I try:
> df = data.frame('id'=c(1,2,3,4),'res'=c(10,10,20,20))
> dfb=df[1:2]
> dfc = df[dfb$id,]

I get something along the lines of what I'd expect where my new
dataframe is a subset of the original based on the matching ids I
specified in dfb$id. Is that wrong in my first example?

Cheers,

Sean

On Thu, Oct 22, 2009 at 4:55 PM, Ista Zahn <istazahn at gmail.com> wrote:
> 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
>>
>> ______________________________________________
>> 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.
>>
>
>
>
> --
> Ista Zahn
> Graduate student
> University of Rochester
> Department of Clinical and Social Psychology
> http://yourpsyche.org
>