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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