Re: [R] system.time gives error when "=" is used for assignment (R-2.6.0)

From: Charles C. Berry <cberry_at_tajo.ucsd.edu>
Date: Thu, 10 Apr 2008 19:09:08 -0700

On Thu, 10 Apr 2008, Kyeongmi Cheon wrote:

> Hello list,
> I found that system.time works correctly when I used "<-" to assign a
> value to a variable but when I happened to use "=" instead of "<-", R
> gave an error message:
> "Error in system.time(your argument here...)". It happened with a few
> functions I tried. Is this a bug or is there any circumstances that
> "=" cannot be used for assignment? Here is a real simple example.

The latter. Although some might say the former, too. And some will no doubt flame me for even saying that. The former, I mean.

Arguments in calls to function (aka arglists) can be in the name=object form.

So,

         (function(x,y) x-y)(y=3,x=2)

evaluates to -1, while

         (function(x,y) x-y)( 3, 2 )

evaluates to 1, as does

          (function(x,y) x-y)(me <- 3, you <- 2) but

          (function(x,y) x-y)(me = 3, you = 2)

gives an error when it tries to match 'me' or 'you' to an argument but fails to find one.

Hint: often

         system.time( { result.of.long.compute <- foo(my.args) } )

is what you want.

HTH, Chuck

p.s. As an exercise for the reader, why does

          (function(x,y) x-y)({me = 3},{you = 2})

not return an error?

>
> fn1 <- function(x) x+1
>
> r1 <- system.time(res1=fn1(2))
> r2 <- system.time(res2 <- fn1(2))
>
>
> Thank you.
> Kyeongmi
> University of Memphis
>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry_at_tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901

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