[R] list of lists, is this element empty

[Duncan Murdoch]

This may be out of context, but on the face of it, this claim is wrong:

On 20/12/2014, 1:57 PM, Boris Steipe wrote:
"Moreover is.na() behaves differently when evaluated on its own, or as
the condition of an if() statement."

The conditions in an if() statement are not evaluated in special
conditions at all.  The only way you'll get a different value is if the
argument to is.na() does tricky stuff like looking at the evaluation stack.

Duncan Murdoch