We are required to write a JavaScript function that generates combinations from n number of arrays with m number of elements in them.
For example −
Consider this data −
const arr = [ [0,1], [0,1,2,3], [0,1,2] ]
3 sub arrays, with a different number of elements in them.
What we want to do is get all combinations by combining an item from each array.
For example −
0,0,0 // item 0 from array 0, item 0 from array 1, item 0 from array 2 0,0,1 0,0,2 0,1,0 0,1,1 0,1,2 0,2,0 0,2,1 0,2,2
And so on.
If the number of arrays were fixed, it would be easy to make a hard-coded implementation. But the number of arrays may vary −
const arr1 = [[0,1], [0,1]]; const arr2 = [[0,1,3,4], [0,1], [0], [0,1]];
Example
The code for this will be −
const arr = [ [0,1], [0,1,2,3], [0,1,2] ] const combineAll = (array) => { const res = []; let max = array.length−1; const helper = (arr, i) => { for (let j=0, l=array[i].length; j<l; j++) { let copy = arr.slice(0); copy.push(array[i][j]); if (i==max) res.push(copy); else helper(copy, i+1); }; }; helper([], 0); return res; }; console.log(combineAll(arr));
And the output in the console will be −
[ [ 0, 0, 0 ], [ 0, 0, 1 ], [ 0, 0, 2 ], [ 0, 1, 0 ], [ 0, 1, 1 ], [ 0, 1, 2 ], [ 0, 2, 0 ], [ 0, 2, 1 ], [ 0, 2, 2 ], [ 0, 3, 0 ], [ 0, 3, 1 ], [ 0, 3, 2 ], [ 1, 0, 0 ], [ 1, 0, 1 ], [ 1, 0, 2 ], [ 1, 1, 0 ], [ 1, 1, 1 ], [ 1, 1, 2 ], [ 1, 2, 0 ], [ 1, 2, 1 ], [ 1, 2, 2 ], [ 1, 3, 0 ], [ 1, 3, 1 ], [ 1, 3, 2 ] ]