[R] looking for something like "ave" I can pass non numeric to

[John Christie]

Hi,
	I have been trying to calculate summary error and coding statistics on 
a by subject basis and seem to be writing a lot of code to do a simple 
thing.  I won't go into my messy version.  What I am asking is if 
anyone knows of a single command that could take the following data and 
get error rates over a given vector.

Given data from ss with,,,

subj	a	rt 	code
1	1	200	good
1	1	321	good
1	2	457	good
1	2	384	bad
2	1	228	good
2	1	343	bad
....

I would like to do a calculation something like ave returns.  An 
artificial example that does not work where I have passed the code 
field to ave is below.

ss$FAcount<- ave(ss$code, ss$subj, function(x) 
length(x[x=="good"])/length(x))