Averaging rows

["Khan, Sohail" <khan@cshl.edu>]

Dear S-Plus Experts,

I have data frame as follows:

ID    ratio_1     ratio_2
X      2.5          2.0 
Y      3.6          2.1
Y      2.9          1.2
Y      3.5          4.2
Z      2.5           1.9
K      0.5           2.1
L       1.4          4.1

I would like average values of columns ratio_1, ratio_2 for all the IDs with 
multiple values, i.e. ID Y would have average ratio_1 = 3.3333, ratio_2.5.
I am a novice S_PLUS user, sorry for the trivial question. Thanks. 


Sohail Khan
Scientific Programmer
COLD SPRING HARBOR LABORATORY
Genome Research Center
500 Sunnyside Boulevard
Woodbury, NY 11797
(516)422-4076