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Hm, a style war on R-Help. I wonder if this goes for long enough, we'll come to
the question of where to put the braces. ;)
Personally, I always use <- instead of = where applicable. In addition to the
distinction between assignment and naming arguments in function calls, it helps
avoid the notorious =/== bug from C programming. Compare
"if(x == 1) {..." /* comparison -- probably what was wanted */
with
"if(x = 1) {..." /* oops */
This has bitten me a number of times in C, so I'd like to avoid it in R/S.
Using "if(identical(x, 1)) {..." also addresses this problem, but that just
looks awkward to me.
--
Hong Ooi
Senior Research Analyst, IAG Limited
388 George St, Sydney NSW 2000
+61 (2) 9292 1566
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Liaw, Andy
Sent: Wednesday, 7 December 2005 7:17 AM
To: '[EMAIL PROTECTED]'; r-help@stat.math.ethz.ch
Subject: Re: [R] R is GNU S, not C.... [was "how to get or store ....."]
From: [EMAIL PROTECTED]
>
> ronggui a écrit :
>
> > I think it is NOT just for historical reason.
> > see the following example:
> >
> >>rm(x)
> >>mean(x=1:10)
> > [1] 5.5
> >>x
> > Error: object "x" not found
>
> x is an argument local to mean(),
> did you expect another answer ?
>
> >>mean(x<-1:10)
> > [1] 5.5
> >>x
> > [1] 1 2 3 4 5 6 7 8 9 10
>
> What is the goal of this "example" ?
I believe it's to show why "<-" is to be preferred over "=" for
assignment...
> Here with "<-",
> (voluntary, or not, side effect)
> the global variable x is, also, created.
> Did the writer really want that ???
Very much so, I believe.
> I though there were other specific statements
> especially intended for global assignment, eg "<<-".
You need to distinguish assignment in function _call_ and assignment in
function _definition_. They ain't the same.
> If this example was intended to prove "<-"
> is better than "="
> ... I'm not really convinced !
In that case, let's try another one (which is one big reason I stopped using
"=" for assignment):
> long.comp <- function(n) {
+ Sys.sleep(n)
+ n
+ }
> result = long.comp(30)
> system.time(result = long.comp(30))
Error in system.time(result = long.comp(30)) :
unused argument(s) (result ...)
> system.time(result <- long.comp(30))
[1] 0.00 0.00 30.05 NA NA
> str(result)
num 30
Cheers,
Andy
>
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