[R] Subset based on items in a list.

Erik Iverson iverson at biostat.wisc.edu
Mon Oct 13 20:44:32 CEST 2008

I don't know if I understand (small example with R command wouuld help), 
but, assuming your data.frame is called 'df'

subset(df, ID %in% ID_list)

Question, is ID_list a "list" or a vector, and are they really "numbers" 
or "factors"?

Kyle. wrote:
> R-help:
> I have a variable ("ID_list") containing about 1800 unique numbers, and a
> 143066x29 data frame.  One of the columns ("ID") in my data frame contains a
> list of ids, many of which appear more than once.  I'd like to find the
> subset of my data frame for which "ID" matches one of the numbers in
> "ID_list." I'm pretty sure I could write a function to do this--something
> like:
> dataSubset<-function(df, id_list){
>     tmp = data.frame()
>     for(i in id_list){
>         for(j in 1:dim(df)[1]){
>             if(i==df$ID[j]){
>                 tmp<-data.frame(df[j,])
>                 }
>             }
>         }
>     tmp
>     }
> but this seems inefficient. As I understand it, the subset function won't
> really solve my problem, but it seems like there must be something out there
> that will that I must be forgetting. Does anyone know of a way to solve this
> problem in an efficient way?  Thanks!
> Kyle H. Ambert
> Graduate Student, Department of Medical Informatics & Clinical Epidemiology
> Oregon Health & Science University
> ambertk at ohsu.edu
> 	[[alternative HTML version deleted]]
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