[R] grouping dataframe entries using a categorical variable

[Ista Zahn]

Hi Bastien,

You can use match(), or the convenience function %in%, like this
(assuming your data.frame is named "dat"):

subset(dat, ESS %in% c("EPB","SAB"))

dat[dat$ESS %in% c("EPB","SAB"), ]

best,
Ista

On Fri, Sep 17, 2010 at 1:02 PM, Bastien Ferland-Raymond
<bastien.ferland-raymond.1 at ulaval.ca> wrote:
>  DearR Users,
>
> I have a problem which I think you might be able to help.  I have a dataframe which I'm trying to "filter" following different groups I specified.  It's a little hard to explain, so here is an example:
>
> My dataframe:
>
>   ESS DHP
> 1  EPB  22
> 2  SAB  10
> 3  SAB  20
> 4  BOJ  14
> 5  ERS  28
> 11 SAB  10
> 12 SAB  22
> 13 BOJ  26
> 20 SAB  10
> 21 SAB  22
> 22 BOJ  32
> 29 SAB  14
> 30 SAB  22
> 38 SAB  14
> 47 SAB  18
>
> I'm trying to filter it by selecting a subgroup of ESS, for example:
>  softwood<- c("EPB","SAB")
>
> So I can obtain:
> NEW dataframe:
>   ESS DHP
> 1  EPB  22
> 2  SAB  10
> 3  SAB  20
> 11 SAB  10
> 12 SAB  22
> 20 SAB  10
> 21 SAB  22
> 29 SAB  14
> 30 SAB  22
> 38 SAB  14
> 47 SAB  18
>
> (my real groups are actually bigger and so are my dataframe but you get the idea).
>
> I have looked at subset and aggregate but it doesn't work and the loop would be totally inefficient. I'm sure there is a function in R that does something like that but I couldn't find the proper "keyword" to search for it.
>
> Thanks for your help,
>
> Bastien
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-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org