From dimitris.rizopoulos at med.kuleuven.be  Tue Mar  7 16:46:03 2006
From: dimitris.rizopoulos at med.kuleuven.be (Dimitris Rizopoulos)
Date: Tue, 7 Mar 2006 16:46:03 +0100
Subject: [Rd] possible bug: NULL equality in lists.
References: <440D9B1E.6020001@vanderbilt.edu><440DA2FE.8050709@statistik.uni-dortmund.de>
	<m2wtf6w9jr.fsf@ziti.local>
Message-ID: <004101c641fe$3d60f1e0$0540210a@www.domain>

I think it'd be more appropriate to use:

sapply(a, "==", "NULL")

or

sapply(a, "==", "NA")

for this case.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Seth Falcon" <sfalcon at fhcrc.org>
To: <r-devel at stat.math.ethz.ch>
Sent: Tuesday, March 07, 2006 4:37 PM
Subject: Re: [Rd] possible bug: NULL equality in lists.


> 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
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 


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[Rd] possible bug: NULL equality in lists.
Dimitris Rizopoulos