R help - Jun 2008 - Creating a list of functions

I've been trying to create a list of function where function[[i]] should
actually return the value of i.

trying:

func <- vector("list",2)
i <- 1
while (i <= 2)
{
func[[i]] <- function()
{
i
}
i <- i+1
}

however only returned the last value of i for each function. Any help how to
achieve the solution intended would be greatly appreciated.

thanks in advance,

andreas posch

Is this what you want:
> func <- vector("list",2)
> i <- 1
> while (i <= 2)
+ {
+     func[[i]] <- local({
+         z <- i
+         function(){ z }
+     })
+     i <- i+1
+ }
> func[[1]]()
[1] 1
> func[[2]]()
[1] 2
>
Your solution was using 'i' which picked up the last definition of
'i'.
'local' create a local copy of 'i' and uses that in the
function.

On Thu, Jun 5, 2008 at 10:50 AM, Andreas Posch <andreas.posch@boku.ac.at>
wrote:
> I've been trying to create a list of function where function[[i]]
should
> actually return the value of i.
>
> trying:
>
> func <- vector("list",2)
> i <- 1
> while (i <= 2)
> {
> func[[i]] <- function()
> {
> i
> }
> i <- i+1
> }
>
> however only returned the last value of i for each function. Any help how
> to achieve the solution intended would be greatly appreciated.
>
> thanks in advance,
>
> andreas posch
>
> ______________________________________________
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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<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?

	[[alternative HTML version deleted]]

On 6/5/2008 10:50 AM, Andreas Posch wrote:
> I've been trying to create a list of function where function[[i]]
should actually return the value of i.
> 
> trying:
> 
> func <- vector("list",2)
> i <- 1
> while (i <= 2)
> {
> func[[i]] <- function()
> {
> i
> }
> i <- i+1
> }
> 
> however only returned the last value of i for each function. Any help how
to achieve the solution intended would be greatly appreciated.
> 
> thanks in advance,
> 
> andreas posch
The problem is that the function definition

function() { i }

has no local variable i, so it looks in the enclosing environment for 
one, and they all find the same one.  The usual way to do what you want 
is to create a builder function, like this:

builder <- function(i) {
   return( function() i )
}

When the anonymous function looks for i, it will find the local one in 
the builder.  Each call to the builder will create a different local 
value of i.

So then your loop would be

while (i <= 2) {
   func[[i]] <- builder(i)
   i <- i + 1
}

I hope this helps.

Duncan Murdoch