[R] count id by id

Denis Kazakiewicz d.kazakiewicz at gmail.com
Tue Jan 18 23:03:11 CET 2011


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? 

Thank you

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