R help - Jun 2017 - is.null(mylist[1]) and is.null(mylist$a) returns different values

Thank you all , very informative, never thought of doing a str( mylist[1] )  

-----Original Message-----
From: "Jeff Newmiller" [jdnewmil at dcn.davis.ca.us]
Date: 06/15/2017 11:56 AM
To: r-help at r-project.org, "Huzefa Khalil" <huzefa.khalil at
umich.edu>, "ce" <zadig_1 at excite.com>
Subject: Re: [R] is.null(mylist[1]) and is.null(mylist$a) returns different
values

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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