Message-ID: <A0558460-B7FC-443C-97E0-4EFF9965595F@gmail.com>
Date: 2012-11-08T14:42:49Z
From: Gonçalo Ferraz
Subject: Accessing selected elements of a list
Hi,
If I have a vector:
junk <- c(2,0,0,3,0)
and want to access, say, all the elements that are greater than zero. I just do:
junk[which(junk>0)]
Now, If I have a list:
jlist <- list(NULL,c(1,0),NULL,c(1,2,3), NULL)
and want to access all the elements that have length greater than zero, I know how to find the elements with:
which(sapply(jlist,length)>0)
But how do I get a new list, only with the non-zero-length elements, without having to write a for loop?
I tried:
notnull <- which(sapply(jlist,length)>0)
jlist[[notnull]]
and got the error:
Error in jlist[[notnull]] : recursive indexing failed at level 2
Thank you for any help!