[R] filling a list faster

[Matthias.Kohl at stamats.de]

another solution:
l <- vector(mode = "list", length = 10^5)
system.time(for(i in (1:10^5)) l[[i]] <- c(i,i+1,i))

On my system this version is even slightly faster than the matrix version ...

Best,
Matthias

----- original message --------

Subject: Re: [R] filling a list faster
Sent: Fri, 13 Jul 2007
From: Philippe Grosjean<phgrosjean at sciviews.org>

> If all the data coming from your iterations are numeric (as in your toy 
> example), why not to use a matrix with one row per iteration? Also, do 
> preallocate the matrix and do not add row or column names before the end 
> of the calculation. Something like:
> 
>  > m <- matrix(rep(NA, 3*10^5), ncol = 3)
>  > system.time(for(i in (1:10^5)) m[i, ] <- c(i,i+1,i))
>     user  system elapsed
>    1.362   0.033   1.424
> 
> That is, about 1.5sec on my Intel Duo Core 2.33Mhz MacBook Pro, compared to:
> 
>  > l <- list("1"<-c(1,2,3))
>  > system.time(for(i in (1:10^5)) l[[length(l)+1]] <- c(i,i+1,i))
>     user  system elapsed
> 191.629  49.110 248.454
> 
> ... more than 4 minutes for your code.
> 
> By the way, what is your "very fast machine", that is actually four 
> times faster than mine (grrrrr!)?
> 
> Best,
> 
> Philippe Grosjean
> 
> ..............................................<?}))><........
>   ) ) ) ) )
> ( ( ( ( (    Prof. Philippe Grosjean
>   ) ) ) ) )
> ( ( ( ( (    Numerical Ecology of Aquatic Systems
>   ) ) ) ) )   Mons-Hainaut University, Belgium
> ( ( ( ( (
> ..............................................................
> 
> Balazs Torma wrote:
> > hello,
> > 
> >     first I create a list:
> > 
> > l <- list("1"<-c(1,2,3))
> > 
> >     then I run the following cycle, it takes over a minute(!) to  
> > complete on a very fast mashine:
> > 
> > for(i in (1:10^5)) l[[length(l)+1]] <- c(i,i+1,i)
> > 
> > How can I fill a list faster? (This is just a demo test, the elements  
> > of the list are calculated iteratively in an algorithm)
> > 
> > Are there any packages and documents on how to use more advanced and  
> > fast data structures like linked-lists, hash-tables or trees for  
> > example?
> > 
> > Thank you,
> > Balazs Torma
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch 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 stat.math.ethz.ch 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.
> 

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