The model: there are two course “A” and “B”; each attended by students of a certain education level. I would like to make a summary table of the factors.
I thought aggregation can do the job, but I am puzzled with counting the factor type of gender. I would like to make a summary of which the output should look like this.

course edu-level gender sum_value
  A     prim      male    <cnt>
  A     prim      female  <cnt>
  A     sec       male    <cnt>
  A     sec       female  <cnt>
...

#    two courses "A" and "B"
module<-as.factor(c(rep("A",5), rep( "B",6)))  
#    gender per course
gender<-as.factor(c(rep("female",2), rep("male",3), rep("female",3), rep("male",3)))
#    education level per gender: primary, secondary or tertiary
edu<-as.factor(c("prim", "sec", "tert", "prim", "sec", "tert","prim", "sec", "tert","prim", "sec"))
course<-data.frame(module, gender, edu)
aggregate(course$gender, list(course$module, course$edu), sum)
# Error in Summary.factor(1:2, na.rm = FALSE) : 
#  ‘sum’ not meaningful for factors