[R] Calculating mean together with split

[Rainer M Krug]

Hi

I have a table called npl containing results of simulations.

It contains about 19000 entries and the structure looks like this:

  NoPlants                  sim run year DensPlants
1        6 lng_cs99_renosterbos   1    4    0.00192
.
.
.


it has 43 different entries for sim and year goes from 1 to 100, and run 
from 1 to 5.

I would like to calculate the mean of DensPlants for each simulation and 
each year seperately, i.e. calculating the mean for all combinations of 
sim and year over run.

I can use

split(npl, npl$sim)

to split npl into different groups each containing the entries for one 
parameterset - but where to go from there?

Rainer

-- 
Rainer M. Krug, Dipl. Phys. (Germany), MSc Conservation
Biology (UCT)

Department of Conservation Ecology and Entomology
University of Stellenbosch
Matieland 7602
South Africa

Tel:		+27 - (0)72 808 2975 (w)
Fax:		+27 - (0)21 808 3304
Cell:		+27 - (0)83 9479 042

email:	RKrug at sun.ac.za
       	Rainer at krugs.de