[R] count number of groups

[R. Michael Weylandt]

length(unique(ID))

Michael

On Fri, May 25, 2012 at 11:38 AM, Charles Determan Jr <deter088 at umn.edu> wrote:
> Hello,
>
> Simple question that I am stuck on and can't seem to find an answer in the
> help files currently.  I have a list which contains repeated ID's.  I would
> like to have R count the number of ID's.  For example:
>
> ID=c(1,1,1,1,2,2,2,2,3,3,3,3)
> as.data.frame(ID)
>
> Clearly, there are 3 groups.  How would I have R give me the summary:
>
> ID
> 3
>
> Many thanks,
> Charles
>
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