[R] filling a list faster

[jim holtman]

Actually if you are really interested in the list, then just do the
lapply and compute your data; it seems to be even faster than the
matrix:

> system.time(l.1 <- lapply(1:10^5, function(i) c(i, i+1, i)))
   user  system elapsed
   0.50    0.00    0.61
> l.1[1:4]
[[1]]
[1] 1 2 1

[[2]]
[1] 2 3 2

[[3]]
[1] 3 4 3

[[4]]
[1] 4 5 4



On 7/13/07, Philippe Grosjean <phgrosjean at sciviews.org> wrote:
> 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
> >
> > ______________________________________________
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> > 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?