[R] NULL object, R programming

[Spencer Graves]

When you set the second attribute of the list to NULL, it actually 
eliminated that attribute, so the length(a) went from 3 to 2.  If you 
don't like that, try the following:

	a <- list(a=3, b=4, c=5)
	a[["b"]] <- NULL
	
You can still refer to the attributes of the list via a[["a"]], 
a[["c"]]], a$a, a$b, etc., and get what you expect even though though 
the length of the list has been reduced.

Spencer Graves
	

Makram Talih wrote:
> Dear R users,
> 
> I get the following (I think puzzling) result when doing the following:
> 
> 
>>a <- list(3,4,5)
>>a[[2]] <- NULL
>>a
> 
> [[1]]
> [1] 3
> 
> [[2]]
> [1] 5
> 
> I would have expected the result to be:
> 
> [[1]]
> [1] 3
> 
> [[2]]
> NULL
> 
> [[3]]
> [1] 4
> 
> as in the outcome of:
> 
> 
>>list(3, NULL, 4)
> 
> 
> Is this a desired effect? If so, could it be built in a 'help(NULL)' file?
> 
> If you think it is relevant, I am using the following R version:
> 
> platform i386-pc-mingw32
> arch     i386           
> os       mingw32        
> system   i386, mingw32  
> status                  
> major    1              
> minor    6.2            
> year     2003           
> month    01             
> day      10             
> language R  
> 
> 
> Many thanks for any clarifications regarding this!
> 
> Regards,
> 
> Makram Talih
> Yale University
> Statistics
> 
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