Re: NA and NaN

[Søren Hauberg]

ons, 12 03 2008 kl. 14:52 +0100, skrev Francesco Potorti`:
> >> I see that Octave has NA, which is described in the manual as "a special
> >> case of the representation of `NaN'".  I do not understand what this
> >> exactly means, because
> >> 
> >> isnan(NA) --> 0
> >Is it? In Octave 3.0.0 I see
> >
> >octave:1> isnan(NA)
> >ans =  1
> 
> Thank you.  I use both Octave 2.1 and Octave 3.0, and I had not tried
> both.  I would appreciate someone to answer my previous questions
> nonetheless, as there is so much code around written for octave 2.1.
In what version do you see that isnan(NA) gives 'false'? I have never
observed this behaviour, so I was quite surprised by your questions.

> However, in light of Søren's observation, would it preferable to use NA
> instad of NaN for missing values?  What about octave-forge packages
> "statistics" and "nan"?  What about Matlab compatibility?
Matlab doesn't have NA, so compatibility can be an issue, depending on
the situation. The interpolation code (eg. 'interp2') uses NA when it
performs extrapolation. In matlab NaN is used. Here there are no
compatibility issues. Personally, I always use NA, when I'm missing
data, and I never really understood how NaN is a good indicator of the
same.

Søren