[R] Summary of data.frame according to colnames and grouping factor

[soeren.vogel at eawag.ch]

A dataframe holds 3 vars, each checked true or false (1, 0). Another  
var holds the grouping, r and s:

### start:example
set.seed(20)
d <- data.frame(sample(c(0, 1), 20, replace=T), sample(c(0, 1), 20,  
replace=T), sample(c(0, 1), 20, replace=T))
names(d) <- c("A", "B", "C")
e <- rep(c("r", "s"), 10)
### end:example

How do I get the count of "1's" (or any other function) applied over  
each var according to the grouping? That is:

Desired output table:

        A      B      C
r  count  count  count
s    ...    ...    ...

or likewise transposed. I'd like to use the table for textual display  
and/or barplot creation.

Thx, Sören

-- 
Sören Vogel, PhD-Student, Eawag, Dept. SIAM
http://www.eawag.ch, http://sozmod.eawag.ch