Multi-dimensional For Loop

Question

I have three arrays and I need to create a set of rules based on these three arrays, but I'm struggling with the logic of how to write a function that will give me every possible combination of every entry in each array. So, I have, for example:

var array 1 = [1, 2];
var array 2 = [3, 4, 5];
var array 4 = [6, 7, 8, 9, 10];

And I'd wan't get back a string, object etc of all possible combinations (which I wont attempt to work out here). So for example:

var result = ["1-3-6", "2-3-6", "1,4,6"];

And so on, so far I've tried sitting down and composing a For Loop but I'm just really not sure where to start. I also looked at maps, but could not find any examples that went this deep, so I wasn't sure if a map would get the job done either.

The actual data I want to load in, the first array has 2 entries, the second have 7 and the last one had 6, so for the workings out I've done there should be 84 entries. That was based on (Array 3 * Array 2) * Array 1.

Hope that all makes sense I know it's a bit confusing. Also worth mentioning that I'm using Angular JS so an angular solution or vanilla JS solution is preferred but not essential.

If I'm guessing right you expect an output array with 84 entries all strings like the example, and the strings should be formed using numbers from the arrays corresponding to their positions. — Dan Philip Bejoy, Sep 07 '17 at 11:04
Possible duplicate of [Cartesian product of multiple arrays in JavaScript](https://stackoverflow.com/questions/12303989/cartesian-product-of-multiple-arrays-in-javascript) — Hassan Imam, Sep 07 '17 at 11:16

score 1 · Accepted Answer · answered Sep 07 '17 at 11:07

What you are looking is the Cartesian product of arrays. You can use a function like this (extracted from here):

function cartesian() {
    var r = [], arg = arguments, max = arg.length-1;
    function helper(arr, i) {
        for (var j=0, l=arg[i].length; j<l; j++) {
            var a = arr.slice(0); // clone arr
            a.push(arg[i][j]);
            if (i==max)
                r.push(a);
            else
                helper(a, i+1);
        }
    }
    helper([], 0);
    return r;
}

There are lot of examples, like:

JavaScript - Generating combinations from n arrays with m elements

With recursive:

Finding All Combinations of JavaScript array values

Cartesian product of multiple arrays in JavaScript

And with multiple (N) arrays:

Combine 2 arrays into 1 in all possible ways in JavaScript

Hope it helps!

Looks very promising I'll chuck it in and have a go with this - thanks :) — Web Develop Wolf, Sep 07 '17 at 12:07

Dan Philip Bejoy · Answer 2 · 2017-09-07T11:18:08.253

1

Nested for loops will do

function arrComb(arr1, arr2, arr3) {
  var l1 = arr1.length,
    l2 = arr2.length,
    l3 = arr3.length,
    i, j, k, res = [];

  for (i = 0; i < l1; i++) {
    for (j = 0; j < l2; j++) {
      for (k = 0; k < l3; k++) {
        res.push(arr1[i] + '-' + arr2[j] + '-' + arr3[k]);
      }
    }
  }
  console.log(res)
}

arrComb([1, 2], [3, 4, 5], [6, 7, 8, 9, 10]);

edited Sep 07 '17 at 11:18

answered Sep 07 '17 at 11:11

Dan Philip Bejoy

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There is no need to cache an arrays length because it's a property that gets updated every time you add an element. It's not a method that counts the elements every time. – Anis Alibegić Sep 07 '17 at 11:14
I could but it rarely makes a difference. The whole snippet is supposed to be a function to be invoked. Did it this way just to demonstrate. – Dan Philip Bejoy Sep 07 '17 at 11:14

score 1 · Answer 3 · answered Sep 07 '17 at 11:32

A bit more elegant:

var array_1 = [1, 2];
var array_2 = [3, 4, 5];
var array_4 = [6, 7, 8, 9, 10];
var result = [];

for (var a1 of array_1)
{
    for (var a2 of array_2)
    {
        for (var a3 of array_4)
        {
            result.push("\""+a1+"-"+a2+"-"+a3+"\"")
        }
    }
}
alert("["+result+"]")

Multi-dimensional For Loop

3 Answers3