[R] filling a list faster

[Balazs Torma]

Thank you all for your answers!

The problem is that I don't know the length of the list in advance!  
And hoped for a convinience structure which reallocates once the  
preallocated list (or matrix) becomes full.

>> By the way, what is your "very fast machine", that is actually four
>> times faster than mine (grrrrr!)?
I don't know the exact parameters of this machine, I just know its  
name is "monster", has 32 GB RAM and >10 CPUs :)

Quoting jim holtman <jholtman at gmail.com>:

> 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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>>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
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>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list
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>> 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?