From ripley@stats.ox.ac.uk  Wed Jul  3 15:28:41 2002
From: ripley@stats.ox.ac.uk (ripley@stats.ox.ac.uk)
Date: Wed, 3 Jul 2002 15:28:41 +0100 (BST)
Subject: POSIX formats have problems with NA (PR#1732)
In-Reply-To: <32525.1025703714@www58.gmx.net>
Message-ID: <Pine.LNX.4.31.0207031524370.6931-100000@gannet.stats>

On Wed, 3 Jul 2002, Jens [ISO-8859-1] Oehlschlgel wrote:

>
> Brian,
>
> Thanks for answering.
>
> > This feature request is already implemented in R-devel.
>
> good to know that it is done in R-devel
>
> > It is not a bug, as why should logical NA be convertible to any other
> > format?
>
> Why then do we have as.character(NA)?

We also have as.character(T) and as.character(F): it's coercion of logicla
vectors which is implemented.

> Isn't it standard, that a as.something() function can handle NAs? Isn't it
> good style to explicitely use as.something(NA) instead of relying on
> auto-coercion? Isn't it a language feature that we can assign NA to any element of a
> vector, especially if NA is a legal (creatable) element?

A POSIXct class (say) is not a vector, strictly. The problem is that `NA'
is a _logical_ vector, and although one can reasonably coerce NA, one
cannot coerce T and F.  So it needs special-case code, and I don't think
you will find it documented anywhere that this needs to work.

Brian

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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POSIX formats have problems with NA (PR#1732)
ripley@stats.ox.ac.uk