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ssippe/cartesianProduct.ts

Created April 20, 2017 00:33
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Typescript Cartesian Product
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cartesianProduct.ts
const f = (a: any[], b: any[]): any[] =>
[].concat(...a.map(a2 => b.map(b2 => [].concat(a2, b2))));
export const cartesianProduct = (a: any[], b: any[], ...c: any[]) => {
if (!b || b.length === 0) {
return a;
}
const [b2, ...c2] = c;
const fab = f(a, b);
return cartesianProduct(fab, b2, c2);
};
@please-rewrite
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please-rewrite commented Oct 31, 2023 •
edited
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Mixed types are tricky.
Give this a try.

The key is [...T]

export const cartesianProduct = <T extends any[][]>(a: [...T]): Array<{[K in keyof T]: T[K][number]}> => a.reduce((a, b) => a.flatMap(d => b.map(e => [d, e].flat())))

@h-chal
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h-chal commented Dec 10, 2025 •
edited
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@please-rewrite 's version with clearer variable names:

export const cartesianProduct = <T extends any[][]>(
    arrays: [...T],
): Array<{ [K in keyof T]: T[K][number]; }> =>
    arrays.reduce((partialProduct, nextArray) =>
        partialProduct.flatMap(items =>
            nextArray.map(
                nextItem => [items, nextItem].flat(),
            )
        )
    );

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