[R] Have a function like the "_n_" in R ? (Automatic count function )

[Charles C. Berry]

On Wed, 25 Feb 2009, Gustaf Rydevik wrote:

> On Wed, Feb 25, 2009 at 3:30 PM, hadley wickham <h.wickham at gmail.com> wrote:
>> And for completeness here's a function that returns the next integer
>> on each call.
>>
>> n <- (function(){
>>  i <- 0
>>  function() {
>>    i <<- i + 1
>>    i
>>  }
>> })()
>>
>>> n()
>> [1] 1
>>> n()
>> [1] 2
>>> n()
>> [1] 3
>>> n()
>> [1] 4
>>> n()
>> [1] 5
>>> n()
>> [1] 6
>>
>>
>> ;)
>>
>> Hadley
>>
>
>
> *headache*!
> I can't wrap my head around this one - too strange code!
> Could someone please give a hint on what's going on?
> How does"i<<- i+1" modify i permanently, seeing as i is defined as 0
> to start with?


i is not _defined_ as zero. It is initially _assigned_ the value of zero 
and is subsequently assigned other values.

As for the details of what goes here, see

 	An Introduction to R
 	Section 10.7 Scope

and study the open.acount()  example there.

HTH,

Chuck

>
> /Gustaf
>
> -- 
> Gustaf Rydevik, M.Sci.
> tel: +46(0)703 051 451
> address:Essingetorget 40,112 66 Stockholm, SE
> skype:gustaf_rydevik
>
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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