[R] If statement generates two outputs

[Berwin A Turlach]

G'day Carl,

On Mon, 23 Mar 2009 20:11:19 -0400
Carl Witthoft <carl at witthoft.com> wrote:

>  >From: Wacek Kusnierczyk <Waclaw.Marcin.Kusnierczyk_at_idi.ntnu.no>
>  >Date: Sun, 22 Mar 2009 22:58:49 +0100
> 
> 
>  >just for fun, you could do this with multiassignment, e.g., using
>  >the (highly experimental and premature!) rvalues:
> 
>  >    source('http://miscell.googlecode.com/svn/rvalues/rvalues.r') 
>  >if (TRUE)
> 
>  >       c(df1, df2) := list(4:8, 9:13)
> 
>  >    dput(df1)
>  >    # 4:8
>  >    dput(df2)
>  >    # 9:13
> 
> 
> -------
> Now THAT's what I call an overloaded operator!   ^_^
> 
> But seriously:  can someone explain to me what's going on in the 
> rvalues.r code?  I tried a simple experiment, replacing ":=" with a 
> "colec" in the code, and of course the line
> 
> c(df1, df2) colec list(4:8, 9:13)
> 
> 
> just gives me a "syntax error" response.   Clearly I need a pointer
> to some documentation about how the colon and equals sign get
> "special treatment somewhere inside R.

Not sure why := gets a special treatment, perhaps because it is not a
valid name and, hence, the parser deduces that it is an operator?

IIRC, the traditional way to define your own operator is to bound the
name by percentage signs, i.e. replacing ":=" by "%colec%" and then
issuing the command

	c(df1, df2) %colec% list(4:8, 9:13)

will work.

Cheers,

	Berwin

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