How deep can/should lists be nested?
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