[MATRIX-SIG] Much ado about nothingness.

[Aaron Watters]

Hey!  Null values!  I had a whole chapter in my
dissertation regarding nulls!

There are many kinds of nulls:
   
   overdefined (computation error)
              |
[normal non-null values here] ...
              |
    unknown/applicable        inapplicable
                 \                      /
                 unknown/maybe-inapplicable

How a query engine or computation should handle this
depends on which one you mean.  However, in general
I think if you want to "layer" null values into a matrix you
might want to use an "indicator mask" which identifies the
null/non-null values as a separate array.

Let me know if this makes sense
----------
From: Hoon Yoon - IPT Quant <hyoon@nyptsrv1.etsd.ml.com>
To: matrix-sig@python.org
Subject: [MATRIX-SIG] Much ado about nothingness.
Date: Tuesday, July 08, 1997 10:18 AM

Hello fellow snake handlers,

  I am attempting to do some Trading (stocks) related number crunching
  in Python. I am having quite a difficulty trying to implement my old
  Gauss logic to Python. It should be dealt in a different way; however,
  my mind is still in the old 2D complete matrix stage that I am finding
  it difficult to find what I wanna to do in Python.
  
  # I have some x period of info into Python lists/arrays. Of course as
  of any financial data there are missing values. So, I stored them as
  None, thinking that None is closest to msg values, but, as some of the
  readers would have realized, none of the nonzero, choose, equal, where, etc...
  can be performed on array or list with None values. I get:
  	TypeError: function not supported for these types, and can't 
  	coerceto supported types
 

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