[R] convert factor dataframe into numeric matrix

[sun]

Bear me if this is a naive question.

I have a dataframe, all lists inside it are factors. When I use 
as.matrix(df) to convert, I get a character matrix while my intention is to 
get numeric matrix. I can make the convertion  iteratively by each list but 
I do think there is some more elegant way of doing this.

please let me know if I missed somthing there.

 Thanks in advance.

Sun