[R] group means of multi-way table?

[Jim Lemon]

On 09/22/2010 08:52 AM, Simon Kiss wrote:
> hello, can someone tell me how to generate the means for a data frame
> that looks like this? My data frame has many more variables, but I won't
> bother you with those; these are the one's that I'm interested in.
> Needless to say, z is the variable in which I'm interested. I'd like to
> find out the mean score of z for NDP managers, Conservative managers and
> Liberal managers and then for a few other configurations.
> Ive played around with aggregate, tapply and by, but I can't get it to
> work.
> Cordially,
> Simon Kiss
> mydata=data.frame(cbind(x,y,z))
> mydata$x=as.factor(sample(c("labourers", "salaried", "managers"),
> size=300, replace=TRUE))
> mydata$y=as.factor(sample(c("NDP", "Green", "Liberal", "Conservative"),
> size=300, replace=TRUE))
> mydata$z=as.numeric(sample(1:4, size=300, replace=TRUE))
>
Hi Simon,
This looks a bit like what brkdn in the prettyR package does. If you 
want the means nested within subgroups, maybe brkdnNest in the plotrix 
package will do what you want.

Jim