[R] Memory management

[yoooooo]

I guess I have more reading to do.... Are there any website that I can read
up on memory management, or specifically what happen when we 'pass in'
variables, which strategy is better at which situation? 

Thanks~
- yoooooooo


Prof Brian Ripley wrote:
> 
> On Tue, 10 Apr 2007, yoooooo wrote:
> 
>>
>> Hi all, I'm just curious how memory management works in R... I need to
>> run an
>> optimization that keeps calling the same function with a large set of
>> parameters... so then I start to wonder if it's better if I attach the
>> variables first vs passing them in (coz that involves a lot of copying..
>> )
> 
> Your paranethetical comment is wrong: no copying is needed to 'pass in' a 
> variable.
> 
>> Thus, I do this
>> fn3 <- function(x, y, z, a, b, c){ sum(x, y, z, a, b, c) }
>> fn4 <- function(){ sum(x, y, z, a, b, c) }
>>
>> rdn <- rep(1.1, times=1e8)
>> r <- proc.time()
>> for (i in 1:5)
>>  fn3(rdn, rdn, rdn, rdn, rdn, rdn)
>> time1 <- proc.time() - r
>> print(time1)
>>
>> lt <- list(x = rdn, y = rdn, z = rdn, a = rdn, b = rdn, c = rdn)
>> attach(lt)
>> r <- proc.time()
>> for (i in 1:5)
>>  fn4()
>> time2 <- proc.time() - r
>> print(time2)
>> detach("lt")
>>
>> The output is
>> [1] 25.691  0.003 25.735  0.000  0.000
>> [1] 25.822  0.005 25.860  0.000  0.000
>>
>> Turns out attaching takes longer to run.. which is counter intuitive
>> (unless
>> the search to the pos=2 envir takes long time as well) Do you guys know
>> why
>> this is the case?
> 
> I would not trust timing differences of that nature: they often depend on 
> the state of the system, and in particular of the garbage collector.
> You should be using system.time() for that reason: it calls the garbage 
> collector immediately before timing.
> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> 
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> 

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