[MATRIX-SIG] Much ado about nothingness.

[Jim Fulton]

Ted Horst wrote:
> 
> Has anybody looked at the Missing type from DigiCool ?  It has the desired
> behavior for arithmetic operations, but doesn't work correctly for math or
> umath functions.  I have no idea how hard this would be to get working, or even
> if this is the proper approach, but somebody else is at least looking at the
> problem.  You can get it from http://www.digicool.com/releases/ExtensionClass/.

Thankyou for mentioning this.  I guess this is the nudge I need to add a
couple of
$0.01.  In part, the Missing module in ExtensionClass is intended to
fulfill a promise I made on this list too long ago.

When I used to work at USGS, I had to deal with missing values alot. 
For my needs, I considered any database or data analysis tool, including
ones I wrote, that didn't make provision for missing data to be almost
useless.  The way I've seen this dealt with is to reserve some special
values (not necessarily IEEE standard ones), as missing values.  One
package I dealt with (P-Stat) actually had three special vallues,
Missing1 (123456e20), Missing2 (123457e20), and Missing3 (123458e20),
that could be used to represent different kinds of missing data.  For
example, this package used Missing3 for things like log(0).  In any
case, all computations had to check for missing values.  While this adds
significantly to the complexity of numerical software, and slightly
reduces it's efficiency, I think the gain is well worth the price.

I think that it would be a good thing for NumPy to reserve one or more
special floating point missing values internally and should expose these
in Python using my (truly trivial) Missing module or something like it.  

I realize that this would be a significant undertaking, although perhaps
there is 
available funding for it.

I feel odd making this suggestion, given that, in my current line of
business, I have little stake in the outcome.

Jim

-- 
Jim Fulton         Digital Creations
jim@digicool.com   540.371.6909
## Python is my favorite language ##
##     http://www.python.org/     ##

_______________
MATRIX-SIG  - SIG on Matrix Math for Python

send messages to: matrix-sig@python.org
administrivia to: matrix-sig-request@python.org
_______________