[Numpy-discussion] how do I list all combinations
Timothy Hochberg
tim.hochberg@ieee....
Wed Dec 26 16:48:18 CST 2007
Here's a baroque way to do it using generated code:
def cg_combinations(seqs):
n = len(seqs)
chunks = ["def f(%s):" % ', '.join('s%s' % i for i in range(n))]
for i in reversed(range(n)):
chunks.append(" " * (n -i) + "for x%s in s%s:" % (i, i))
chunks.append(" " * n + " yield (" + ', '.join('x%s' % i for i in
range(n)) + ')')
code = '\n'.join(chunks)
exec code
return f(*seqs)
It should be reasonably fast, if non-obvious. I've included a version with
some timing and testing against Chucks version below. Enjoy.
(Also, it can be simplified slightly, but I wanted to generate in the same
order as Chuck for comparison purposes).
======================================================================
def count(seqs) :
counter = [0 for i in seqs]
maxdigit = [len(i) - 1 for i in seqs]
yield counter
while True :
i = 0;
while i < len(counter) and counter[i] >= maxdigit[i] :
counter[i] = 0
i += 1
if i < len(counter) :
counter[i] += 1
yield counter
else :
return
def count_combinations(seqs):
for c in count(seqs):
yield tuple(s[i] for (s, i) in zip(seqs, c))
def cg_combinations(seqs):
n = len(seqs)
chunks = ["def f(%s):" % ', '.join('s%s' % i for i in range(n))]
for i in reversed(range(n)):
chunks.append(" " * (n -i) + "for x%s in s%s:" % (i, i))
chunks.append(" " * n + " yield (" + ', '.join('x%s' % i for i in
range(n)) + ')')
code = '\n'.join(chunks)
exec code
return f(*seqs)
a = "abcde"*10
b = range(99)
c = [x**2 for x in range(33)]
seqs = [a, b, c]
if __name__ == "__main__":
assert list(count_combinations(seqs)) == list(cg_combinations(seqs))
import timeit
test = timeit.Timer('list(count_combinations(seqs))',
'from __main__ import count_combinations, seqs')
t1 = test.timeit(number=10)
test = timeit.Timer('list(cg_combinations(seqs))',
'from __main__ import cg_combinations, seqs')
t2 = test.timeit(number=10)
print t1, t2
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