[Bf-python] Hashing Vectors

[Martin Poirier]

--- Joe Eagar <joeedh at gmail.com> wrote:

> Campbell Barton wrote:
> > Hi, There are a few scripts I have that I use a
> dict for vertex 
> > locations, so as not to double up on locations as
> an example
> >
> > vert_dict[tuple(vertex.co)]= vertex.index
> >
> > It would be nicer and faster if the 2,3, or 4 
> floats could be hashed, 
> > any hints as to hashing a vector and possibly a
> matrix type?
> >
> Well, python ints do have unlimited length. So, you
> could simply times 
> the coordinates by a fixed amount (say, 1000) to
> retain a reasonable 
> amount of precision, convert them to ints, then pack
> the coordinates 
> into a giant integer (96 bits or so :D ).
> 
> Um.  that'd be:
> 
> 
> int1 = int(x*1000.0)
> int2 = int(x*1000.0)
> int3 = int(x*1000.0)
> hash = int1 + (int2 << 32) + (int3 << 64)


Errr, just make a tuple of the floats then, no need to
mess around like that.

The problem is not that they are floats, the problem
is that vector objects are mutable.

This is only a problem if you want to use vectors as
dict keys or as part of a set.

Making a tuple out of them is *the* way to solve that.
Making vector immutable is not a viable option (due to
how wrapped vectors currently work).

Martin

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