[R] binary coding of NA, Nan etc.

[Prof Brian Ripley]

On Fri, 28 Sep 2001, Laurent Gautier wrote:

> Hello,
>
>
> Thanks to the Pr. Ripley for the precise explanations.
> Not so long long ago, I have been generating numerical binary data file
> using java, and noticed that Double.NaN in java was just something very
> big (1.797693e+308) when read in R through readBin. Being too lazy/in a
> hurry to look for the reason I just turned the values greater than or
> equal to that into NA when read in R.
> As that is a rather dirty way of doing things, and as I am ignorant in
> numbers binary representation, I was thinking a paramater to readBin or
> writeBin specifying the convention wanted for the could be nifty.
>
> Does it makes (any) sense ?

How would you specify it?  You would need a way to specify the bit pattern
(of the source or target endianness?) of Inf, -Inf, NA, the class of NaNs
(there are many of them) for doubles and perhaps floats too.  And R
has no type to represent such bit patterns.

I would expect all compiled languages to be using the same representations
on modern hardware.  However, Java is not in that sense compiled and may
well be different: I have no idea.

One thing I did not say before: R's standard NA is the NaN with low word
of 1954.  I have no idea how to generate that on another system except
via the sort of sneaky tricks arithmetic.c plays.  The multiplicity
of NaNs complicates this enormously.

-- 
Brian D. Ripley,                  ripley at 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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