R help - Sep 2004 - [R/S] strange

Dear R and S People:

I have run across something very strange.  Here is a function that I wrote
for R:

boot1 <- function(y,method="f",p=1) {
n1 <- length(y)
n2 <- n1*p
n3 <- n2 - 1
a <- 0.5*(outer(1:n3,1:n3,function(x,y){n2 - pmax(x,y)}))
return(a)
}

and here is the R output:
> y1
[1] 9 8 7 3 6
> source("boot1.R")
> boot1(y=y1,p=4)
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
[,15] [,16] [,17] [,18] [,19]
 [1,]  9.5  9.0  8.5  8.0  7.5  7.0  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [2,]  9.0  9.0  8.5  8.0  7.5  7.0  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [3,]  8.5  8.5  8.5  8.0  7.5  7.0  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [4,]  8.0  8.0  8.0  8.0  7.5  7.0  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [5,]  7.5  7.5  7.5  7.5  7.5  7.0  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [6,]  7.0  7.0  7.0  7.0  7.0  7.0  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [7,]  6.5  6.5  6.5  6.5  6.5  6.5  6.5  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [8,]  6.0  6.0  6.0  6.0  6.0  6.0  6.0  6.0  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
 [9,]  5.5  5.5  5.5  5.5  5.5  5.5  5.5  5.5  5.5   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
[10,]  5.0  5.0  5.0  5.0  5.0  5.0  5.0  5.0  5.0   5.0   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
[11,]  4.5  4.5  4.5  4.5  4.5  4.5  4.5  4.5  4.5   4.5   4.5   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
[12,]  4.0  4.0  4.0  4.0  4.0  4.0  4.0  4.0  4.0   4.0   4.0   4.0   3.5   3.0
2.5   2.0   1.5   1.0   0.5
[13,]  3.5  3.5  3.5  3.5  3.5  3.5  3.5  3.5  3.5   3.5   3.5   3.5   3.5   3.0
2.5   2.0   1.5   1.0   0.5
[14,]  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0  3.0   3.0   3.0   3.0   3.0   3.0
2.5   2.0   1.5   1.0   0.5
[15,]  2.5  2.5  2.5  2.5  2.5  2.5  2.5  2.5  2.5   2.5   2.5   2.5   2.5   2.5
2.5   2.0   1.5   1.0   0.5
[16,]  2.0  2.0  2.0  2.0  2.0  2.0  2.0  2.0  2.0   2.0   2.0   2.0   2.0   2.0
2.0   2.0   1.5   1.0   0.5
[17,]  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5   1.5   1.5   1.5   1.5   1.5
1.5   1.5   1.5   1.0   0.5
[18,]  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0   1.0   1.0   1.0   1.0   1.0
1.0   1.0   1.0   1.0   0.5
[19,]  0.5  0.5  0.5  0.5  0.5  0.5  0.5  0.5  0.5   0.5   0.5   0.5   0.5   0.5
0.5   0.5   0.5   0.5   0.5
> 
which is as it should be.

Now I tried the same thing in S+
> y1
[1] 9 8 7 3 6
> source("boot1.R")
> boot1(y=y1,p=4)
Problem in FUN(rep(X, length(Y)), rep(Y, each = length(X))): Object
"n2" not found
Use traceback() to see the call stack
> 
I have no idea why it works in R but not in S+.

R 1.9.1 for Windows
S+ Version 6.2 for Windows.
Any help is appreciated!

Is this part of the difference in scoping, please?

Sincerely,
Erin M. Hodgess
Associate Professor
Dept. of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: hodgesse at uhd.edu

Erin Hodgess <hodgess at gator.uhd.edu> writes:
> Dear R and S People:
> 
> I have run across something very strange.  Here is a function that I wrote
> for R:
> 
> boot1 <- function(y,method="f",p=1) {
>   n1 <- length(y)
>   n2 <- n1*p
>   n3 <- n2 - 1
>   a <- 0.5*(outer(1:n3,1:n3,function(x,y){n2 - pmax(x,y)}))
>   return(a)
> }
[and it doesn't work in S]

Well, if you didn't understand what lexical scoping was about before,
now is your chance... 

n2 is in the lexical scope of the (unnamed) function that is getting
passed to outer(), because the function is defined in (the environment
of) the call to boot1. Therefor the value of n2 is available inside
that function.

S doesn't have lexical scoping. Instead it has "frame 0" and
"frame
1", which can be used as "scratchpads" for routines to scribble
pieces
of information on. So a not-quite-so-dirty variant of your solution is
to assign n2 to frame 1, rather than as permanent data. Not the only
solution, obviously.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907