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
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