R devel - Oct 2012 - How deep can/should lists be nested?

I started idly wondering how deeply lists could be nested, and
couldn't find an explicit limit in the documentation.  With this
simple test

a_list <- list()
count <- 0
repeat
{
  a_list[[1]] <- a_list
  count <- count + 1
}

my (Win7, R-2.16.0 devel) machine threw an error when count got close to 25000.

The error that stopped it was

Error: protect(): protection stack overflow

I don't know how easy it would be to stop such an error occuring, and
it probably isn't that useful to be able to nest lists any further.  I
do think it might be useful for users to be able to know how deeply
they can nest lists though.

Perhaps it would be better to limit nesting to the value of
getOption("expressions").  Does anyone have any strong feelings on
what the correct behaviour should be?

--
Regards,
Richie

live-analytics.com
4dpiecharts.com

On 12-10-14 7:06 AM, Richard Cotton wrote:
> I started idly wondering how deeply lists could be nested, and
> couldn't find an explicit limit in the documentation.  With this
> simple test
>
> a_list <- list()
> count <- 0
> repeat
> {
>    a_list[[1]] <- a_list
>    count <- count + 1
> }
>
> my (Win7, R-2.16.0 devel) machine threw an error when count got close to
25000.
>
> The error that stopped it was
>
> Error: protect(): protection stack overflow
>
> I don't know how easy it would be to stop such an error occuring, and
> it probably isn't that useful to be able to nest lists any further.  I
> do think it might be useful for users to be able to know how deeply
> they can nest lists though.
>
> Perhaps it would be better to limit nesting to the value of
> getOption("expressions").  Does anyone have any strong feelings
on
> what the correct behaviour should be?
There should be no limit other than memory.  That overflow you saw is a 
bug.  Not sure it's worth fixing, since 25000 is far beyond any sensible 
nesting level, but I'll take a look.

Duncan Murdoch