is.na(v)<-b (was: Re: [R] Beginner's query - segmentation fault)

[Simon Fear]

Well, that's a convincing argument, but maybe 
it's the name that's worrying some of us. Maybe it would be 
more intuitive if called set.na (sorry, I mean setNA).

Also "is.na<-" cannot be used to create a new variable of 
NAs, so is not a universal method,  which is a shame for its 
advocates.

I note also that for a vector you can assign a new NA using 
either TRUE or FALSE:

> a <- 1:3
> is.na(a[4])<-F
> a
[1]  1  2  3 NA

For a list,  assigning F leaves the "new" element set to NULL.

Mind you, I suspect this would be a particularly stupid thing 
to do, so I'm not going to lose any sleep over R's reaction to it.

> 
> -----Original Message-----
> From: Prof Brian Ripley [mailto:ripley at stats.ox.ac.uk]
> I don't think it can ever `go wrong', but it can do things other than
> the 
> user intends.  The intention of is.na<- is clearer, and so 
> perhaps user 
> error is less likely?  That is the thinking behind the 
> function, anyway.
 

Simon Fear
Senior Statistician
Syne qua non Ltd
Tel: +44 (0) 1379 644449
Fax: +44 (0) 1379 644445
email: Simon.Fear at synequanon.com
web: http://www.synequanon.com
 
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