gvrocha gvrocha - 2 months ago 12
Python Question

How to apply itertools.product to elements of a list of lists?

I have a list of arrays and I would like to get the cartesian product of the elements in the arrays.

I will use an example to make this more concrete...

itertools.product seems to do the trick but I am stuck in a little detail.

arrays = [(-1,+1), (-2,+2), (-3,+3)];


If I do

cp = list(itertools.product(arrays));


I get

cp = cp0 = [((-1, 1),), ((-2, 2),), ((-3, 3),)]


But what I want to get is

cp1 = [(-1,-2,-3), (-1,-2,+3), (-1,+2,-3), (-1,+2,+3), ..., (+1,+2,-3), (+1,+2,+3)].


I have tried a few different things:

cp = list(itertools.product(itertools.islice(arrays, len(arrays))));
cp = list(itertools.product(iter(arrays, len(arrays))));


They all gave me cp0 instead of cp1.

Any ideas?

Thanks in advance.

Answer
>>> list(itertools.product(*arrays))
[(-1, -2, -3), (-1, -2, 3), (-1, 2, -3), (-1, 2, 3), (1, -2, -3), (1, -2, 3), (1, 2, -3), (1, 2, 3)]

This will feed all the pairs as separate arguments to product, which will then give you the cartesian product of them.

The reason your version isn't working is that you are giving product only one argument. Asking for a cartesian product of one list is a trivial case, and returns a list containing only one element (the list given as argument).

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