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Re: Difference between NaN and NA?
From: |
John W. Eaton |
Subject: |
Re: Difference between NaN and NA? |
Date: |
Thu, 8 Apr 2010 07:15:36 -0400 |
On 8-Apr-2010, Jaroslav Hajek wrote:
| On Thu, Apr 8, 2010 at 9:03 AM, David Bateman <address@hidden> wrote:
| > Jaroslav Hajek wrote:
|
| > Exact.. NaN is flagged by a particular exponent in IEEE754, so there are
| > many values of the mantissa that still give a NaN.
Right, I added this feature to Octave specifically for compatibility
with NA in R. The idea was to be able to exchange binary data with R
and preserve the special NaN value that R uses for NA.
| In the current situation, NA's do no harm in Octave, but they're also
| not much useful, because most functions ignore them, for instance,
| mean ([1,2,3,NA]) is NA etc.
| On the contrary, inserting checks for NA's everywhere is a good idea
| either, because it will slow things down for everyone.
Yes, I assume R has a lot of special checks for NA (and that you meant
"is not a good idea". Un?fortunately, no one was ever motivated to
make Octave functions NA-aware. So the value exists, but it is not
really used for anything.
Also, there is no guarantee that NA will be preserved across a
function call. For example, on some platforms, you might see
something like
sin (NA) ==> NaN
because it might be implemented with something like
double sin (double x)
{
if (isnan (x))
return NaN;
...
}
instead of
double sin (double x)
{
if (isnan (x))
return x;
...
}
So even ensuring that NA is preserved would add overhead...
But I still do like the idea of having NA separate from NaN so that
you can have a way to express "missing data" that is separate from
"failed calculation". But I don't know of any really great way to
implement it.
jwe
- Difference between NaN and NA?, Matthias Brennwald, 2010/04/08
- Re: Difference between NaN and NA?, Søren Hauberg, 2010/04/08
- Re: Difference between NaN and NA?, Jaroslav Hajek, 2010/04/08
- Re: Difference between NaN and NA?, David Bateman, 2010/04/08
- Re: Difference between NaN and NA?, Søren Hauberg, 2010/04/09
- Re: Difference between NaN and NA?, Jaroslav Hajek, 2010/04/09
- Re: Difference between NaN and NA?, Søren Hauberg, 2010/04/09
- Re: Difference between NaN and NA?, Jaroslav Hajek, 2010/04/09
- Re: Difference between NaN and NA?, Søren Hauberg, 2010/04/09
- Re: Difference between NaN and NA?, Matthias Brennwald, 2010/04/09
- Re: Difference between NaN and NA?, Søren Hauberg, 2010/04/09