R devel - Mar 2006 - possible bug: NULL equality in lists.

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'


If I create a list with a NULL value
  >a <- alist(NULL, "bob", c(3,6,2,3))
  >a
[[1]]
NULL

[[2]]
[1] "bob"

[[3]]
c(3, 6, 2, 3)

and run some tests on 'a', the '== "NULL' test returns TRUE
for the NULL
entry in the list 'a'.
  >a == 'NULL'
[1]  TRUE FALSE FALSE
  >a == "NULL"
[1]  TRUE FALSE FALSE
  >a == 'cat'
[1]  FALSE FALSE FALSE

This is consistent for every example of NULL's in a list that I can 
think of.

Is this a bug or undocumented correct behavior?

Here is my version output

platform i486-pc-linux-gnu
arch     i486
os       linux-gnu
system   i486, linux-gnu
status
major    2
minor    2.0
year     2005
month    10
day      06
svn rev  35749
language R


Thanks

Charles
-- 
Charles Dupont	Computer System Analyst		School of Medicine
		Department of Biostatistics	Vanderbilt University

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:

   sapply(a, is.null)

Uwe Ligges


> If I create a list with a NULL value
>   >a <- alist(NULL, "bob", c(3,6,2,3))
>   >a
> [[1]]
> NULL
> 
> [[2]]
> [1] "bob"
> 
> [[3]]
> c(3, 6, 2, 3)
> 
> and run some tests on 'a', the '== "NULL' test returns
TRUE for the NULL
> entry in the list 'a'.
>   >a == 'NULL'
> [1]  TRUE FALSE FALSE
>   >a == "NULL"
> [1]  TRUE FALSE FALSE
>   >a == 'cat'
> [1]  FALSE FALSE FALSE
> 
> This is consistent for every example of NULL's in a list that I can 
> think of.
> 
> Is this a bug or undocumented correct behavior?
> 
> Here is my version output
> 
> platform i486-pc-linux-gnu
> arch     i486
> os       linux-gnu
> system   i486, linux-gnu
> status
> major    2
> minor    2.0
> year     2005
> month    10
> day      06
> svn rev  35749
> language R
> 
> 
> Thanks
> 
> Charles