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-   -   n-dim permutation matrix/generator? (http://www.velocityreviews.com/forums/t396564-n-dim-permutation-matrix-generator.html)

 robert 11-20-2006 01:37 PM

n-dim permutation matrix/generator?

for the purpose of flat n-dim iteration a function or generator ndim_permute(*v) should compute or generate a list of tuples like:

ndim_permute( (0,1,2), (0,1), (0,1), ) ->

0 0 0
0 0 1
0 0 2
0 1 0
0 1 1
0 1 1
1 0 1
.....

what is a good solution? Or is there already a total iterator existing somewhere in the stdlib?

robert

 Anton Vredegoor 11-20-2006 02:26 PM

Re: n-dim permutation matrix/generator?

robert wrote:

> for the purpose of flat n-dim iteration a function or generator
> ndim_permute(*v) should compute or generate a list of tuples like:
>
> ndim_permute( (0,1,2), (0,1), (0,1), ) ->
>
> 0 0 0
> 0 0 1
> 0 0 2
> 0 1 0
> 0 1 1
> 0 1 1

hmm ... shouldn't his be (0 1 2) ?

> 1 0 1
> ....
>
>
> what is a good solution? Or is there already a total iterator existing
> somewhere in the stdlib?

I think there are good solutions in the python cookbook at:

http://aspn.activestate.com/ASPN/Cookbook/Python

But it gives a page mentioning 'system difficulties' now, so I can't
check. Someone else will post the link to their favorite recipe.
Meanwhile, this gives me a chance to plug some of my experimental code :-)

A.

def ncycle(seq,n):
while True:
for x in seq:
for dummy in xrange(n):
yield x

def cross(*args):
p,R = 1,[]
for arg in args:
L = list(arg)
R.append(ncycle(L,p))
p *= len(L)
R.reverse()
for dummy in xrange(p):
yield tuple(x.next() for x in R)

def test():
for x in cross((0,1,2), (0,1), (0,1)):
print x

if __name__=='__main__':
test()

 guenter.jantzen@prodv.de 11-20-2006 05:13 PM

Re: n-dim permutation matrix/generator?

If your products are not too big you may use the following approach

def cross(*L):
P=[()]
for i in range(len(L)):
P_=[]
for p in P:
for el in L[i]:
P_.append(p+(el,))
P = P_
return P

if __name__ == '__main__':
for x in cross((0,1,2), (0,1), (0,1)):
print x

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