[R] new R-user needs help

[antoniababe at yahoo.se]

Dear all,

I have a dataset 

Exp name id x1 x2 x3 x4 x5 
1   a    1  23 24 23 22 30
1   b    2  25 26 27 23 24
1   c    3  32 19 23 25 28
2   a    4  28 32 24 26 27
2   b    5  23 24 25 26 28
2   c    6  23 31 30 38 23
3   a    7  24 25 31 27 29
3   b    8  28 25 26 32 28 
3   c    9  21 31 28 23 29

where each name a,b and c is repeated three times.
Now I want to calculate the the averages of a,b and c
over the three experiments for each x. For example for
x1 I want to calculate the average of a like

[a(from exp1) + a(exp2)+ a(exp3)]/3= (23+28+24)/3

How can I do that ?

Thanks for your help,
Regards,

Antonia