R help - Jul 2007 - using the function unique(), but asking it to ignore a column of a data.frame

Take for example the following data.frame:

a<-c(1,1,5)
b<-c(3,2,3)
c<-c(5,1,5)
sample.data.frame<-data.frame(a=a,b=b,c=c)

I'd like to be able to use unique(sample.data.frame), but have
unique() ignore column a when determining the unique elements.

However, I figured that this would be setting for incomparables=, but
it appears that this funcationality hasn't been incorporated.  Is
there a work around for this, i.e. to be able to get unique to only
look at selected columns of a data frame?

Thanks,
Andrew

On 7/9/07, Andrew Yee <yee at post.harvard.edu>
wrote:
> Take for example the following data.frame:
>
> a<-c(1,1,5)
> b<-c(3,2,3)
> c<-c(5,1,5)
> sample.data.frame<-data.frame(a=a,b=b,c=c)
>
> I'd like to be able to use unique(sample.data.frame), but have
> unique() ignore column a when determining the unique elements.
>
> However, I figured that this would be setting for incomparables=, but
> it appears that this funcationality hasn't been incorporated.  Is
> there a work around for this, i.e. to be able to get unique to only
> look at selected columns of a data frame?
unique(df[,c("a","c")]) ?

Hadley