I'm trying to build/find a function, which will give me all combinations for N number of elements.
The solution below gives me an answer for pairs (i.e. 2 elements).
I'd like to parameterize it, so that I can define the number of combined elements (e.g. 3 elements => ['one', 'two', 'three'], ['one', 'two', 'four'], ... , 4 elements, and so on.
(Bonus internet points if you can tell me the name what I'm looking for (cartesian-product?)!)
var array = ['one', 'two', 'three', 'four', 'five']
// get pairs
var result = array => array.flatMap((v, i) => array.slice(i+1).map( w => [v, w] ));
console.log(result(array))
// output:
// [
// ["one", "two"],
// ["one", "three"],
// ["one", "four"],
// ["one", "five"],
// ["two", "three"],
// ["two", "four"],
// ["two", "five"],
// ["three", "four"],
// ["three", "five"],
// ["four", "five"]
// ]
I think this is your solution.
/**
* Usage Example:
*
* console.log(combination(['A', 'B', 'C', 'D'], 2, true)); // [[ 'A','A' ], [ 'A', 'B' ]...] (16 items)
* console.log(combination(['A', 'B', 'C', 'D'])); // [['A', 'A', 'A', 'B' ],.....,['A'],] (340 items)
* console.log(comination(4, 2)); // all posible values [[ 0 ], [ 1 ], [ 2 ], [ 3 ], [ 0, 0 ], [ 0, 1 ], [ 0, 2 ]...] (20 items)
*/
function combination(item, n) {
const filter = typeof n !=='undefined';
n = n ? n : item.length;
const result = [];
const isArray = item.constructor.name === 'Array';
const pow = (x, n, m = []) => {
if (n > 0) {
for (var i = 0; i < 4; i++) {
const value = pow(x, n - 1, [...m, isArray ? item[i] : i]);
result.push(value);
}
}
return m;
}
pow(isArray ? item.length : item, n);
return filter ? result.filter(item => item.length == n) : result;
}
console.log("#####first sample: ", combination(['A', 'B', 'C', 'D'], 2)); // with filter
console.log("#####second sample: ", combination(['A', 'B', 'C', 'D'])); // without filter
console.log("#####third sample: ", combination(4, 2)); // just number