[R] detecting NULL in recursive lists
Charles C. Berry
cberry at tajo.ucsd.edu
Tue Mar 10 00:56:53 CET 2009
On Mon, 9 Mar 2009, Vadim Ogranovich wrote:
> Dear R-users,
> How can I detect a NULL in a recursive list?
> For a regular list I could use lapply:
>> lapply(list(x=NULL), is.null)
>  TRUE
> However that doesn't work for structures like list(list(x=NULL)). I tried rapply but it treats NULL as a list and discards them:
>> rapply(list(a=1, b=list(x=NULL)), is.null)
> Any suggestion?
Is this what you want?
> foo <- function(x) sapply(x, function(x) if (is.list(x)) foo(x) else length(x)==0,simplify=FALSE)
> foo(list(a=list(A=1:2,B=NULL), b=list(C=NULL,D=1)))
> Thank you for your help,
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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