From sfalcon at fhcrc.org  Tue Mar  7 16:37:12 2006
From: sfalcon at fhcrc.org (Seth Falcon)
Date: Tue, 07 Mar 2006 07:37:12 -0800
Subject: [Rd] possible bug: NULL equality in lists.
In-Reply-To: <440DA2FE.8050709@statistik.uni-dortmund.de> (Uwe Ligges's
	message of "Tue, 07 Mar 2006 16:13:02 +0100")
References: <440D9B1E.6020001@vanderbilt.edu>
	<440DA2FE.8050709@statistik.uni-dortmund.de>
Message-ID: <m2wtf6w9jr.fsf@ziti.local>

Uwe Ligges <ligges at statistik.uni-dortmund.de> writes:

> Charles Dupont wrote:
>
>> I was messing around with R and I found an example R behaving oddly:
>> 
>> a <- alist(NULL, "bob", c(3,6,2,3))
>> a
>> a == 'NULL'
>> a == "NULL"
>> a == 'cat'
>> 
>
>
> Always use is.null() to test on NULL, as in:

What should I do if I want to check for the string "NULL"?

> a <- list(NULL, "NULL", NA, "NA")

> a == "NULL"
[1]  TRUE  TRUE FALSE FALSE

> a == "NA"
[1] FALSE FALSE  TRUE  TRUE

These are because of as.character:

> as.character(a)
[1] "NULL" "NULL" "NA"   "NA"  

Yet,

> as.character(NULL)
character(0)
> as.character(NA)
[1] NA



+ seth



[Rd] possible bug: NULL equality in lists.
Seth Falcon