[R] count id by id

[David Winsemius]

On Jan 18, 2011, at 5:03 PM, Denis Kazakiewicz wrote:

>
> Hi
>
> Trying to work out that:
> Each person can take from 1 to 9 drugs. And data frame looks like
>
>
> id	drug
> 1	d
> 2	g
> 2	d
> 2	r
> 3	e
> 3	a
> ...........
>
> Q: How many drugs one person takes on average?

Something like:

mean(
   with(dfrm,
        tapply(drug, id, length), na,rm=TRUE)
     ) )

(Not sure if the na.rm is needed , but it cannot hurt)
>


-- 

David Winsemius, MD
West Hartford, CT