Re: [Numpy-discussion] can this be made faster?

[Charles R H. <cha...@gm...>]

On 10/9/06, A. M. Archibald <per...@gm...> wrote:
>
> > > > > c contains arbitray floats.
> > > > > essentially it is to compute class totals
> > > > > as in total[class[i]] += value[i]
>
> > > This seems like a rather common operation - I know I've needed it on
> > > at least two occasions - is it worth creating some sort of C
> > > implementation? What is the appropriate generalization?
> >
> > Some sort of indirect addressing infrastructure. But it looks like this
> > could be tricky to make safe, it would need to do bounds checking at the
> > least and would probably work best with a contiguous array as the
> target. I
> > could see some sort of low-level function called argassign(target,
> indirect
> > index, source) that could be used to build more complicated things in
> > python.
>
> If it were only assignment that was needed, fancy indexing could
> already handle it. The problem is that this is something that can't
> *quite* be done with the current fancy indexing infrastructure - every
> time an index comes up we want to add the value to what's there,
> rather than replacing it. I suppose histogram covers one major
> application; in fact if histogram allowed weightings ("count this
> point as -0.6") it would solve the OP's problem.


Sure, just add functions arg_addassign, etc., which means dest[ind[i]] +=
src[i], just as arg_assign would mean dest[ind[i]] = src[i]. If you covered
all the assign variants I think you could do most everything. Upper level
python routines could deal with shaping and such while the lower level
routines dealt with flat, contiguous arrays.

Chuck