[Bf-python] Hashing Vectors

[Campbell Barton]

Martin Poirier wrote:
> --- Campbell Barton <cbarton at metavr.com> wrote:
>
>   
>> If hashing a vector at its current state is evil,
>> could there be a way to...
>> a) Speed up conversion to a tuple? - not sure how
>> this might be done, 
>> have a vec.tuple() function to avoid python
>> iterating over 2,3,4 axis 
>> for every conversion.
>>     
>
> Did you try doing it manually? You'll always know in
> advance the number of dimensions you're dealing with,
> so just do:
>
> (v[0], v[1], v[2]) instead of tupple(v)
>
>
>   
>> b) Have a method that returns a non tuple hashable 
>> hashable type - 
>> somthing like vec.key() which could return a long
>> int or whatever ends 
>> up being best to hash. - document that this is
>> location dependant and 
>> will change of the location changes.
>>     
>
> It would have to be tupple based, that is pretty much
> the cleanest way to make an immutable vector, short of
> packing everything non-destructively in an int.
>
>   
>> c) Have a new iterator datatype for vector arrays,
>> with functions like 
>> adding a unique vector, and other useful operations-
>> such an array would 
>> be  useful for Blender.Geometry
>>     
>
>
> A Vector Set.
>
> Thinking about this rang a bell though. Vector's are
> floating point data, so any test done on equality is
> potentially wrong due to float errors.
>
> Martin
>
>   

For vector arrays (sets would be unordered) and append function could 
have an optional error margin.
vec_array.append(vec, 0.0001)

The way Im using them at the moment dosent create float errors but your 
right.


Benchmarked conversion without hashing, here are the results

0.623914957047  # tuple()
0.396674871445  #  (x,y,z)
0.44420599937  # ([0], [1], [2])

0.59113907814 # tuple()
0.375689983368  #  (x,y,z)
0.433271884918  # ([0], [1], [2])
0.509349107742  # (x,y,z) - from a function



--
from Blender import Mesh, sys
me= Mesh.Get('Cube')
verts= me.verts

t= sys.time()
for v in me.verts:
        co= v.co
        i= tuple(co)
print sys.time()-t

t= sys.time()
for v in me.verts:
        co= v.co
        i= (co.x, co.y, co.z)
print sys.time()-t

t= sys.time()
for v in me.verts:
        co= v.co
        i= (co[0], co[1], co[2])
print sys.time()-t



def vec_tuple3d(v):
        return v.x, v.y, v.z

t= sys.time()
for v in me.verts:
        co= v.co
        i= vec_tuple3d(co)
print sys.time()-t
--



-- 
Campbell J Barton

133 Hope Street
Geelong West, Victoria 3218 Australia

URL:    http://www.metavr.com
e-mail: cbarton at metavr.com
phone: AU (03) 5229 0241