[R] behavior of [<-.foo

From: Armstrong, Whit <whit.armstrong_at_hcmny.com>
Date: Fri 22 Sep 2006 - 18:39:48 GMT


Can someone help me understand the following behavior of "[<-" ?

If I define a simple class based on a matrix, the [<- operation only inserts into the first column:

> x <- matrix(rnorm(10),nrow=5,ncol=2)
>  class(x) <- "foo"
> "[<-.foo" <- function(x, i, j, value) {
+     if(missing(i)) i <- 1:nrow(x)
+     if(missing(j)) j <- 1:ncol(x)
+ 
+     x <- unclass(x)
+     x <- NextMethod(.Generic)
+     class(x) <- "foo"
+     x

+ }
> 
> x[] <- 100.0
> x
     [,1]       [,2]

[1,] 100 -0.1465296
[2,] 100 -0.2615796
[3,] 100 -0.8882629
[4,] 100 -0.2886357
[5,] 100 -0.9565273

attr(,"class")
[1] "foo"

Based on the behavior of [<- for a matrix, I would have thought that the data for the whole object would be replaced.

for instance:

> y <- matrix(rnorm(10),nrow=5,ncol=2)
> y

            [,1] [,2]
[1,] -0.55297049 -1.1896488
[2,] 0.06157438 -0.6628254

[3,] -0.28184208 -2.5260177
[4,] 0.61204398 -0.3492488
[5,] 0.43971216 1.8990789

> y[] <- 100
> y

     [,1] [,2]
[1,] 100 100
[2,] 100 100
[3,] 100 100
[4,] 100 100
[5,] 100 100

>

Thanks,
Whit

code for above:

x <- matrix(rnorm(10),nrow=5,ncol=2)
x
 class(x) <- "foo"
"[<-.foo" <- function(x, i, j, value) {

    if(missing(i)) i <- 1:nrow(x)
    if(missing(j)) j <- 1:ncol(x)
    x <- unclass(x)
    x <- NextMethod(.Generic)
    class(x) <- "foo"
    x
}
x[] <- 100.0
x

> R.Version()
$platform
[1] "i686-pc-linux-gnu"

$arch
[1] "i686"

$os
[1] "linux-gnu"

$system
[1] "i686, linux-gnu"

$status
[1] ""

$major
[1] "2"

$minor
[1] "3.1"

$year
[1] "2006"

$month
[1] "06"

$day
[1] "01"

$`svn rev`
[1] "38247"

$language
[1] "R"

$version.string
[1] "Version 2.3.1 (2006-06-01)"

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