R devel - Jun 2006 - NAs in unsplit factor

R-devel,

Below is a simple example calling split and unsplit on a numeric
vector of length 2 where 'f' is c(1,NA).
> unsplit(split(c(1,2), c(1,NA)), c(1,NA))
[1] 1 0

I noticed that the call to vector in unsplit gives us 0 as the 2nd
element of the result.

Is this the intended result, as opposed to NA?

Thanks for your help,

Jeff

-- 
Jeff Enos
Kane Capital Management
jeff at kanecap.com

[Jeff Enos]
>Below is a simple example calling split and unsplit on a numeric
>vector of length 2 where 'f' is c(1,NA).
>> unsplit(split(c(1,2), c(1,NA)), c(1,NA))
>[1] 1 0
>I noticed that the call to vector in unsplit gives us 0 as the 2nd
>element of the result.
>Is this the intended result, as opposed to NA?
?unsplit says:

  'unsplit' reverses the effect of 'split'.

and later explains:

  'unsplit' returns a vector for which 'split(x, f)' equals
'value'

So some may argue that, while not necessarily intended, that this is at 
least not unintended :-).  Yet, why "0" is chosen here, among a myriad
of possibilities?  "NA", as you suggest, might be a more neutral
choice.

-- 
Fran?ois Pinard   http://pinard.progiciels-bpi.ca