is.null(mylist[1]) and is.null(mylist$a) returns different values
By the way, NULL is not a "null list", it has class (and type and mode) "NULL" not "list". "NULL" is an odd class, in that it can have only one instance and hence can never have any attributes. "list" objects, like other vector objects, may have length zero, but such objects are not the same as NULL. Bill Dunlap TIBCO Software wdunlap tibco.com On Thu, Jun 15, 2017 at 8:56 AM, Jeff Newmiller <jdnewmil at dcn.davis.ca.us> wrote:
I find that the str function is more helpful for understanding the difference between a null list and a list containing a null list than the implicit print function call that the interpreter invokes when you enter an expression at the console. str( mylist[1] ) -- Sent from my phone. Please excuse my brevity. On June 15, 2017 8:39:47 AM PDT, Huzefa Khalil <huzefa.khalil at umich.edu> wrote:
Hi, Try
is.null(mylist[[1]])
[1] TRUE Notice the double square brackets. From: ?`[` "The most important distinction between [, [[ and $ is that the [ can select more than one element whereas the other two select a single element." On Thu, Jun 15, 2017 at 11:33 AM, ce <zadig_1 at excite.com> wrote:
Hi I have a list : mylist <- list( a = NULL, b = 1, c = 2 )
mylist[1]
$a NULL
is.null(mylist[1])
[1] FALSE
is.null(mylist$a)
[1] TRUE why? I need to use mylist[1]
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