[R] how to do by-processing using weighted.mean

[Denis Chabot]

Hi,

I'd like to compute the weighted mean of some variables, all using the 
same weight variable, for each combination of 3 factor variables.

I found how I could use "summarize" (from Hmisc) to do normal means for 
combinations of 3 factors, but I cannot find a way of doing weighted 
means. Is it possible in R?

Thanks in advance,

Denis Chabot