R help - Oct 2003 - is.na(v)<-b (was: Re: Beginner's query - segmentation fault)

> -----Original Message-----
> From: Richard A. O'Keefe [mailto:ok at cs.otago.ac.nz]
<snip>
> The very existence of an "is.na<-" which accepts  a logical
> vector containing FALSE as well as TRUE ...
And don't forget this is not the only usage of is.na<-. In fact it is 
designed to take any valid indexing value. For example:
> a<-1:10
> is.na(a) <- 1:5
> a
 [1] NA NA NA NA NA  6  7  8  9 10

Wow. I really hate that. Someone tell me again why this is
better than a[1:5] <- NA ??
 

Simon Fear
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Syne qua non Ltd
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By accident I'm also toying around with NA's, so I started reading up on
this thread but failed to find a 'concluding' remark or advice. As a
naive
R user I would have loved to see a comment "do it like this".

The prevailing opinion seemed to be that is.na() might be better (safer) 
but x <- NA is much clearer to understand. Can I relatively safely use the 
easy form, or is it better to remember (the hard way) the safer version? 
Has the discussion continued privately or just stopped here?

Personally I still find the fragments below (taken from the thread) very 
counter intuitive, not to say scary.

x <- 1:10
is.na(x) <- 1:5

and

is.na(x) <- FALSE


It's very hard to understand what happens (as layman) because the 
assignment seems to reverse in meaning in the first example (actually 
taking indices 1:5 of x and assigning those the value NA) whereas in the 
second case it's not obvious what happens to x: will it get the value FALSE 
or will the original value remain(*).

IMHO the <- NA construct is much easier to understand and should be made 
safe in all possible situations (whatever the underlying safety problem or 
other difficulties might be).


kind regards,
Paul

(*) Such a remark will probably lead to some kind of reprimand because it's 
probably somewhere within the 10e6 manual pages but I'm trying my luck here.


-- 
Paul Lemmens
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