[R] Integer vs numeric

[Christophe Genolini]

x[c(2,4)] work as well

Henrik Bengtsson a écrit :
> x[1:n]
>
> /H
>
> On Jan 29, 2008 5:07 AM,  <cgenolin at u-paris10.fr> wrote:
>   
>> Seems strange to me to define an operator relatively to a very special case.
>> I have to admit that I do not use 1:1e7 every day :-)
>>
>> Wouldn't it be more appropriate to define a a:b operator numeric (that
>> is preserving the initial class of a and b) and in specific case that
>> need optimization, changing the type?
>>
>> for i in as.integer(1:1e7)
>>
>> That might appears as a minor point, but when using S4, for what I
>> know, if you define a class that can take either 1:3 or c(1,3,4), one
>> is integer, the other numeric, one of those will not be accepted by the
>> class...
>>
>> Christophe
>>
>>
>>
>>     
>>> On 28-Jan-08 22:40:02, Peter Dalgaard wrote:
>>>       
>>>> [...]
>>>> AFAIR, space is/was more of an issue. If you do something like
>>>>
>>>> for i in 1:1e7
>>>>     some.silly.simulation()
>>>>
>>>> then you have 40 MB sitting there doing nothing, and 80 MB if
>>>> it had been floating point.
>>>>         
>>> Hmmm ... there's something to be said for good old
>>>
>>>  for(i=1,i<=1e7,i++){....}
>>>
>>> As pointed out in ?"for", when you do
>>>
>>>  for(i in X){...}  #(e.g. X=(1:1e7))
>>>
>>> the object X is created (or is already there) in full
>>> at the start and sits there, as you say doing nothing,
>>> until you end the loop. Whereas the C code just keeps
>>> track of i and of the condition.
>>>
>>> At least on a couple of my machines (64MB and 184MB RAM)
>>> knocking out 40MB would inflict severe trauma! Let alone 80MB.
>>> Mind you, the little one is no longer allowed to play with
>>> big boys like R, though the other one is still used for
>>> moderate-sized games.
>>>
>>> Would there be much of a time penalty in implementing
>>> a 'for' loop, C-style, as
>>>
>>>  i<-1
>>>  while(i<=1e7){
>>>    ...
>>>    i<-i+1
>>>  }
>>>
>>> ??
>>>
>>> It looks as though there might be:
>>>
>>>  system.time(for(i in (1:1e7)) x<-cos(3) )
>>>  #[1] 13.521  0.132 13.355  0.000  0.000
>>>  system.time({i<-1;while(i<=1e7){x<-cos(3);i<-i+1}})
>>>  #[1] 38.270  0.076 37.629  0.000  0.000
>>>
>>> which suggests that the latter is about 3 times as slow.
>>> (And no, this wasn't done on either of my puny babes).
>>>
>>> (And this isn't the first time I've wished for an R
>>> implementation of "++" as a CPU-level incrementation,
>>> as opposed to the R-arithmetic implementation which
>>> treats "adding 1 to a variable" as a full-dress
>>> arithmetic parade!
>>>
>>> Best wishes,
>>> Ted.
>>>
>>> --------------------------------------------------------------------
>>> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
>>> Fax-to-email: +44 (0)870 094 0861
>>> Date: 28-Jan-08                                       Time: 23:34:52
>>> ------------------------------ XFMail ------------------------------
>>>
>>>       
>>
>> ----------------------------------------------------------------
>> Ce message a ete envoye par IMP, grace a l'Universite Paris 10 Nanterre
>>
>>
>> ______________________________________________
>> R-help at 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.
>>
>>     
>
>