On Oct 17, 2014, at 1:06 AM, PO SU wrote:
>
> Tks for your alternative way's details. but like you mentioned in graphics
> package, i still wonder how to overload an operator which can pass one param
> like +2 .
> There seems exists some examples for my needing. But i try to find them but
> without any results.
> can you show me some examples from it?
>
I think this might be a case of "if you don't know enough to do it, then you
don't know why you shouldn't do it." (Or vice versa?) I did search for a
relevant fortune to support my impression, but the various entries for
fortune("parse") and fortune("eval") didn't seem to hit the mark.
library(ggplot2)
help(pack="ggplot2") # scroll to bottom of page
ggplot2:::`+.gg` # this shows the S3 method of adding an operator based on
the S3 method dispatch.
I was able to emulate that example to create a C-like, unary `+` operator for a
new class, but I'm not willing to put it in print for fear that my karmic
account might be depleted.
--
David.
> --
>
> PO SU
> mail: desolato...@163.com
> Majored in Statistics from SJTU
>
>
>
> At 2014-10-17 15:16:47, "David Winsemius" <dwinsem...@comcast.net> wrote:
>>
>> On Oct 16, 2014, at 10:36 PM, PO SU wrote:
>>
>>>
>>> Tks for your advice, let the ++ problem alone, how to write an
>>> Unary operator ? Is it permitted in R?
>>> such as a<-2 , a%+2% will let a be 4 .
>>
>> OK, that's just wrong. Oh, OK, just for fun, as it were:
>>
>> inc <- function(x)
>> {
>> eval.parent(substitute(x <- x + 1))
>> }
>>
>>
>>> inc(10)
>> Error in 10 <- 10 + 1 : invalid (do_set) left-hand side to assignment
>>> y=10
>>> inc(y)
>>> y
>> [1] 11
>>
>>
>>> I just want to know it , i won't pollute r with it , because i know
>>> what is r . : )
>>>
>> It's certainly permitted. Just look at all the overloadings of the "+"
>> operator in graphics packages. Look up the documentation on methods in
>> R.
>>
>> Why not just use a well-behaved function, though?
>>
>> .inc <- function(x) x+1
>>> .inc(10)
>> [1] 11
>>
>> Then you won't be tempted to try 10 <- .inc(10) because it just
>> wouldn't make sense.
>>
>> --
>> David.
>>
>>> --
>>>
>>> PO SU
>>> mail: desolato...@163.com
>>> Majored in Statistics from SJTU
>>>
>>>
>>>
>>>
>>> At 2014-10-17 13:09:47, "Rolf Turner" <r.tur...@auckland.ac.nz> wrote:
>>>> On 17/10/14 17:29, PO SU wrote:
>>>>>
>>>>> Dear expeRts,
>>>>> Now i want to know how to implement an Unary operator like i++
>>>>> in cpp's synax form.
>>>>> e.g. 2++ will let 2 be 3 , a<-2 ,a++ ,will let a be 3
>>>>> I tried this :
>>>>> '%++%'<-function(x){
>>>>> x<<-x+1
>>>>> }
>>>>> but it have problem, the biggest one is it seems the function need
>>>>> twoparams like a%++%b , how to write a function needing just one
>>>>> param?
>>>>>
>>>>> TKS !
>>>>
>>>> Just ***DON'T***. The "++" operator is useful only for those wish to
>>>> write code which is obscure to the point of incomprehensibility. It
>>>> makes C and its offspring "write only" languages.
>>>>
>>>> If you are going to use R, use R and don't pollute it with such
>>>> abominations.
>>>>
>>>> cheers,
>>>>
>>>> Rolf Turner
>>>>
>>>>
>>>> --
>>>> Rolf Turner
>>>> Technical Editor ANZJS
>>> ______________________________________________
>>> R-help@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> David Winsemius, MD
>> Alameda, CA, USA
>>
David Winsemius
Alameda, CA, USA
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