This is not really OO at all, in my opinion. It's an example of the
amazing flexibility of the language.
I'd like to add on to what Erik said, with an example:
sum(1:10)
[1] 55
foo <- sum
foo(1:10)
[1] 55
junk <- list(a=sum)
junk$a(1:10)
[1] 55
sum is an R object; it happens to be a function.
When I do
foo <- sum
I'm creating another R object. It's also a function, so I use it with
the same syntax.
When I do
junk <- list(a=sum)
I'm creating another R object. It's a list, and its first element,
named 'a', is a function.
Since the element is a function, I use it just like any other
function, i.e, follow its name with a pair of parentheses with
arguments between them.
Note that in the last example it doesn't matter what the other
elements in the list, if any, are. I could just as well do
junk <- list( foo=data.frame(x=1:4), b=c('x','y'), dd=sum)
Then
junk$dd(1:10)
junk$dd( junk$foo$x )
are valid statements. There's no connection between using 'junk' both
inside the parentheses and outside. Since junk$dd is a function, you
can supply it with any R object, and it doesn't matter where that R
object comes from.
I doubt that it's documented in the way you might be expecting. It's
a result of the generality of list elements -- they can be any R
object.
Hope this helps.
-Don
At 10:48 PM +0100 5/12/10, Ted Harding wrote:
Greetings All,
Out of curiosity, I've just done a very primitive experiment:
Obj <- list(Fun=sum, Dat=c(1,2,3,4))
Obj$Fun(Obj$Dat)
# [1] 10
That sort of thing (much more sophisticated) must be documented
mind-blowingly somewhere. Where?
Where I stand right now: The above (and its immediately obvious
generalisations, like Obj$Fun<-cos) is all I know about it so far.
Ted.
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E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 12-May-10 Time: 22:48:14
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Don MacQueen
Environmental Protection Department
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