Re: Data Manipulation

["Richard M. Heiberger" <rmh@temple.edu>]

I think you want tapply

> tmp <- data.frame(a=c(1,2,3,1,1,2), b=c("a","a","b","b","b","c"),
+ d=factor(c(1,2,1,2,2,1)))
> tmp
  a b d 
1 1 a 1
2 2 a 2
3 3 b 1
4 1 b 2
5 1 b 2
6 2 c 1
> tapply(tmp$a, tmp[,c("b","d")], mean)
  1  2 
a 1  2
b 3  1
c 2 NA
>

This says that the average of the b="a" and d=1 cells is 1.

etc