[R] Function for subset of cases/lines

[Stefan Uhmann]

Hi,

I have a vector:

q1<-c(4660,5621,5629,8030,8080,8180,8501,8190,8370,8200)

The following command gives me the mean of its elements:

mean(q1)
[1] 7346.1

What can I do to do the same for the variable 'height', but only for the 
cases/rows which have one of the elements of q1 as 'number':

   number height
1 4660	2.5
2 5010	1.4
3 5621	0.8
4 5629	2.3
5 8030	2.5
6 8080	2.4
7 8090	0.9
8 8180	1.4
9 8501	1.2
10 8190	1.9
11 8200	2.0
12 8370	2.1
13 8200	1.8

Thanks for any help,
Stefan