Subset based on items in a list.

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

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