[Numpy-discussion] Anyone have a well-tested SWIG-based C++ STL valarray <=> numpy.array typemap to share?

Christopher Barker Chris.Barker@noaa....
Wed Sep 5 13:45:57 CDT 2007


Bill Spotz wrote:
> Yes, this resizing memory management issue is the main reason I haven't 
> tried to implement it in numpy.i yet.

> <thinking out loud>
> A possibly better solution would be to develop a class that inherits 
> from std::valarray<TYPE> but also implements the array interface 
> attributes (these attributes would have to be dynamic, in that they 
> check the std::valarray attributes when accessed rather than storing 
> copies).

I like that, though it's way over my head to implement.

However, I'm beginning to have my doubts about valarrays. I'm reading:

Josuttis, Nicolai M. 1999. "The C+= Standard Library: A Tutorial and 
Reference"

It's 8 years old now, but he writes:

"The valarray classes were not designed very well. In fact, nobody tried 
to determine if the specification worked"

He goes on to suggest that Blitz++ might have more of a future. (though 
it looks like he's involved with the Boost project now)

He also points out some major flaws in the text. In reading, I also see 
that while valarrays can be used for multidimensional arrays, the 
semantics are pretty ugly.

However, he also says: "In principle...you can change their size. 
However, changing the size of a valarray is provided only to make a 
two-step initialization (creating and setting the size)"

So maybe the memory re-allocation is such an issue.

Does anyone know the status of support for valarrays now?

Is there another alternative? At the moment, all we need is a one-d 
fixed size array. There is Boost::array (and MultiArray), but Boost has 
always seemed like a big, ugly, hard to build dependency. Can you just 
grab the code for some of these small pieces by themselves?

-Chris

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Christopher Barker, Ph.D.
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