[R] Summarizing counts by multiple factors

[Noah Silverman]

Hi,

An example data set is:

group    level    color
A        1        "blue"
A        1        "Red"
B        1        "blue"
B        2        "Red"
A        2        "Red"
B        2        "Red"
B        2        "blue"
B        2        "blue"
A        2        "blue"
A        2        "Red"


I'd like to compute a summary of counts for each combination of group, 
level, color.

An example output would be something like this:
group    level    color        count
A        1        "blue"        1
A        2        "red"        2
B        2        "red"        2
etc..


The tapply function seems to do this for a single variable, but I can 
figure out to to do it for combinations of more than one factor.  I also 
see the ave function, but can't figure out how to apply it to multiple 
factors.

Any suggestions?

Thanks