[BioC] How do you sort the differentially expressed genes?

[De-Jian ZHAO]

Dear members,

I am seeking for an efficient way to sort the genes into different 
categories.

I am working on the analysis of the microarray data and now I encounter a 
problem. After getting the differentially expressed genes, I want to sort 
them into different categories according to their functions. However, I find 
it hard to set up a criteria to classify them. Now I am trying to employ the 
KEGG Orthology to facilitate the sortation, but the genes without the KO 
entries become homeless. I wonder  how you sort the genes. Furthermore, if 
anyone has used the GO Slim to classify the genes, please give a comment on 
it. 

Thank you.