[R] Using match.arg() with list of functions?

[Michael Friendly]

I have a function of two arguments, (m, n) that returns a list with the 
same structure as the function makefoo below.
When m=1, it returns a list of vectors, each of length n.
When m>1, it returns a list of square matrices, each of size m x m.

makefoo <- function(m, n) {
     if (m==1) {
         A <- sample(1:100, n)
         B <- sample(1:100, n)
         C <- sample(1:100, n)
     }
     else {
         A <- B <- C <- list(rep(0, n))
         for (i in seq(n)) {
             A[[i]] <- matrix(sample(1:100, m^2), m, m)
             B[[i]] <- matrix(sample(1:100, m^2), m, m)
             C[[i]] <- matrix(sample(1:100, m^2), m, m)
         }
     }
     result <- list(m=m, A=A, B=B, C=C)
     class(result) <- "foo"
     result
}

I'd like to define an as.data.frame function for class "foo" object that 
applies either det() or tr() to the matrices
in the case m>1.  The function below works, but I'd rather define the 
argument FUN as c(det, tr) and use
something like match.arg(FUN) to determine which was supplied. Is there 
some easy way to do this?

# matrix trace
tr <- function(M) sum(diag(M))

# why can't I use FUN=c(det, tr) & match.arg(FUN) below?
as.data.frame.foo <- function(x, FUN=det) {
     m <- x$m
     if(m==1) df <- with(x, data.frame(A, B, C))
     else {
#        FUN <- match.arg(FUN)
         A <- unlist(lapply(x$A, FUN))
         B <- unlist(lapply(x$B, FUN))
         C <- unlist(lapply(x$C, FUN))
         df <- data.frame(A, B, C)
         colnames(df) <- paste(deparse(substitute(FUN)), c("A", "B", 
"C"), sep="")
         }
     df
}

### Test cases ####

 > foo1 <- makefoo(1, 4)
 > as.data.frame(foo1)
    A  B  C
1 38 86 49
2 67 65  2
3 41 46 82
4 59  8 78
 >

 > foo2 <- makefoo(2, 4)
 > as.data.frame(foo2)
    detA  detB  detC
1  -342 -5076 -2621
2 -4712  1568 -1724
3 -4491 -1892 -2768
4  2990 -5448  2974
 > as.data.frame(foo2, FUN=tr)
   trA trB trC
1 118  65  80
2  62  85  99
3 108  86  98
4 110  23 129
 >




-- 
Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    Web:   http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA