[SciPy-user] arrays with units

Robert Kern robert.kern at gmail.com
Tue Jun 27 20:05:55 CDT 2006

Alexander Ross wrote:
> I'm in need of a simple way to attach units of measurement to a numpy  
> array.  I've read some of the previous discussion on the topic, and  
> found the constants module tucked away in the sandbox. While the  
> constants package does a good job at providing access to the various  
> physical constants it doesn't satisfy my needs. 

Which are?

> The package Unum  
> would require me to use object arrays, and I don't want to do that.

I don't think so.


> Ideally, I'd like an extended ndarray adding a new attribute  
> `units'.  The `units' attribute would be updated by the appropriate  
> arithmetic operations, and I guess exceptions would be raised for  
> operations which don't make sense.
> Is anything like this in the works? Should I strike out on my own?

Not particularly. Most unit packages work well with arrays; instead of 
inheriting from ndarray, they simply hold an attribute that is assumed to be a 
number-like object (like an array). Some may still need to be ported from 
Numeric to numpy:

Konrad Hinsen's Scientific.Physics.PhysicalQuantities
Michael Aivazis's pyre.units
Enthought's enthought.units (mostly derived from Michael's work)

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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