[R] multiple assignments ?

[Bert Gunter]

On Tue, Aug 24, 2010 at 8:45 AM, Maas James Dr (MED) <J.Maas at uea.ac.uk> wrote:
> Thanks Bert, will have a look.  I'm originally a Fortran programmer so tend to think in loops ... so yes expect it may be job for loops, just tried to avoid it

 because several references say not to use loops in R.

-- Yes, an unfortunate misunderstanding. The references refer mostly
to the unnecessary use of loops at the R (interpreted) level -- which
also includes _apply type constructs -- vs inbuilt vectorization,
which are loops at the C level and so orders of magnitude faster and
cleaner code, to boot. An example would be what you might be doing
following the Fortran paradigm:

## warning BAAAD R code
myvec <- vector("numeric", 1E5)
for(i in 1:(1E5))myvec[i] <- sin(i)

versus

myvec <- sin( (1:(1E5))) ## because sin() is vectorized


But conventional use of looping (often better --cleaner code, data
structures-- in their list versions: lapply, mapply, tapply,...) at
the interpreted R level is perfectly apporpriate; the only caveat
being that they can apparently bog down if the number of loops is
"very" large, perhaps > 1E5 or more. I have never actually experienced
such problems, however, so can't really speak to them.

-- Bert


>
> I note your helpful comments about lists, will see if I can do it that way!
>
> Will check this out, thanks
>
> Jim
>
>
> ===============================
> Dr. Jim Maas
> Research Associate in Network Meta-Analysis
> School of Medicine, Health Policy and Practice
> CD Annex, Room 1.04
> University of East Anglia
> Norwich, UK
> NR4 7TJ
>
> +44 (0) 1603 591412
>
>
> -----Original Message-----
> From: Bert Gunter [mailto:gunter.berton at gene.com]
> Sent: Tuesday, August 24, 2010 4:39 PM
> To: r.ookie
> Cc: Maas James Dr (MED); r-help at r-project.org
> Subject: Re: [R] multiple assignments ?
>
> None of this would work if the list is long. Isn't this an obvious
> task for a loop, explicit or implicit?
>
> e.g.
>
> for(i in 1:100)assign(paste("vec",i,sep=""), vector("integer",5))
>
> or probably better because it creates a list structure:
>
> ## warning, untested. You may have to fool with the syntax a bit:
>
> listofempties <- lapply(1:100, vector,mode="integer",length=5)
>
> ## you can name the components with names(listofempties) <-
> paste("vec",1:100,sep="")
>
> HOWEVER, I rather doubt that any of this is necessary: that is, it is
> rarely necessary or wise in R to first create empty objects and then
> populate them. Using lists and list operations usually allows both to
> be done more efficiently and conveniently in one step.
>
> --
> Bert Gunter
> Genentech Nonclinical Statistics
>
> On Tue, Aug 24, 2010 at 8:19 AM, r.ookie <r.ookie at live.com> wrote:
>> Do you mean something like this?
>>
>>>
>>  n <- 5
>>
>>>
>>  (vec1 <- matrix(rep(1, n)))
>>     [,1]
>> [1,]    1
>> [2,]    1
>> [3,]    1
>> [4,]    1
>> [5,]    1
>>
>>>
>>  (vec2 <- matrix(rep(2, n)))
>>     [,1]
>> [1,]    2
>> [2,]    2
>> [3,]    2
>> [4,]    2
>> [5,]    2
>>
>>>
>>  (vec3 <- matrix(rep(3, n)))
>>     [,1]
>> [1,]    3
>> [2,]    3
>> [3,]    3
>> [4,]    3
>> [5,]    3
>>
>>>
>>
>>
>>>
>>  (vec <- matrix(c(vec1, vec2, vec3)))
>>      [,1]
>>  [1,]    1
>>  [2,]    1
>>  [3,]    1
>>  [4,]    1
>>  [5,]    1
>>  [6,]    2
>>  [7,]    2
>>  [8,]    2
>>  [9,]    2
>> [10,]    2
>> [11,]    3
>> [12,]    3
>> [13,]    3
>> [14,]    3
>> [15,]    3
>>
>>>
>>
>> On Aug 24, 2010, at 4:58 AM, Maas James Dr (MED) wrote:
>>
>> Simple one, have read and googled, still no luck!
>>
>> I want to create several empty vectors all of the same length.
>>
>> I would like multiple empty vectors (vec1, vec2, vec3) and want to create them all in one line.
>>
>> I've tried
>>
>> vec1,vec2,vec3 <- vector(length=5)
>> and
>> c(vec1,vec2,vec3) <- vector(length=5)
>>
>> and several other attempts but nothing seems to work ... suggestions?
>>
>> Thanks
>>
>> Jim
>>
>> ===============================
>> Dr. Jim Maas
>> University of East Anglia
>>
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> 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.
>>
>> ______________________________________________
>> 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.
>>
>