[R] how to bind lists recursively

[Bill.Venables at csiro.au]

This is somewhat subtle.

Rolf's solution (here corrected to...)

a <- list()
for(i in 0:10000) a[[i+1]] <- i

is the best of the loop solutions (or at least the best I know of).  The
apparently similar

a <- list(0)
for(i in 1:10000) a <- c(a, list(i))

will take a lot longer, although the result is the same.  For example:

> system.time({
    a <- list()
    for(i in 0:10000) a[[i+1]] <- i
    })
   user  system elapsed 
   0.59    0.00    0.59 
> system.time({
    a <- list(0)
    for(i in 1:10000) a <- c(a, list(i))
    })
   user  system elapsed 
   6.87    0.00    6.89 
>

That's a factor of about 11 times as long.  The best of the lot is

a <- as.list(0:10000)

of course, but this has problems with generalisation, (which everyone
suspects is going to be needed here...).

Bill Venables.  



-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Rolf Turner
Sent: Wednesday, 28 May 2008 1:02 PM
To: Daniel Yang
Cc: r-help at r-project.org
Subject: Re: [R] how to bind lists recursively


On 28/05/2008, at 2:43 PM, Daniel Yang wrote:

> Dear all,
>
> I want to create a list that contains 0,1,2,3, ..., 10000 as its  
> elements. I used the following code, which apparently doesn't work  
> very well.
>
> a <- 0
> for(i in 1:10000) {
>    a <- list(a, i)
> }
>
> The result is not what I wanted. So how to create the bind lists  
> recursively so that the last element would be the newly added one  
> while the previous elements all remain the same?

a <- list()
for(i in 1:10000) a[[i]] <- i

(The word ``bind'' is inappropriate.)

	cheers,

		Rolf Turner

######################################################################
Attention:\ This e-mail message is privileged and confid...{{dropped:9}}

______________________________________________
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.