Summary: how do arguments work?

[Carlisle Thacker <thacker@aoml.noaa.gov>]

Thanks to all who replied!  My problem was not passing the argument to
by(), which was needed for function used within by():

                             | specified here
                             v
> test.fcn <- function(a, b, x){
+   by(a, b, function(data, x) x*data, x)}
                            ^          ^
                            |          | MUST ALSO BE HERE!
                            |
                            | needed here

> test.a <- data.frame(u = 1:4,v = c(1,1,2,2))
> test.a
  u v
1 1 1
2 2 1
3 3 2
4 4 2
> test.fcn(test.a, test.a$v, 3)
b:1
  u v
1 3 3
2 6 3
------------------------------------------------------------
b:2
   u v
3  9 6
4 12 6