[R] Coding for contrasts in unbalanced designs

[Guillaume Brutel]

Sorry for possible cross posting but it seems that my previous message was send as HTML and then scrubbed.

Dear list members,

I want to use a GLM with an unbalanced factor and continuous variables.
My factor F has 12 unbalanced levels:
F=as.factor(c('A','B','C','C','C','C','D','D','D','D','D','D','E','E','E','E','E','E','F','G','G','H','I','I','J','J','J','K','L','L','L'))
> summary(F)
A B C D E F G H I J K L 
1 1 4 6 6 1 2 1 2 3 1 3

I thus want to code contrasts appropriatly.
I have looked in R documentations and R-help archives without finding the information for unbalanced designs.
Any help will be very useful.
Thanks you very much.
Guillaume Brutel.