javascript iterate through and map a multi-dimensional array

Question

I want to apply a function to each of the values at all levels of the array:

arr = [[1,2,3],[1,2,3],[[1,2],[1,2]],1,2,3]

for example, multiply all the values by 3, and map it in the same format as before so I get:

arr = [[3,6,9],[3,6,9],[[3,6],[3,6]],3,6,9]

What would be the best way to go about this?

I tried to use a recursive function:

function mapall(array){
         array.map(function(obj){
                   if (Array.isArray(obj)===true) { return mapall(obj) }
                   else{ return obj*3 }
                   })
            };

but when I run it I just get undefined, so I must be doing something not quite right??

Any ideas??

Thanks

Joseph · Accepted Answer · 2015-07-17 13:37:57Z

4

Everything was working, but you forgot to return from array.map. Here's a cleaner version of your code:

var arr = [[1,2,3],[1,2,3],[[1,2],[1,2]],1,2,3];
function mapAll(array){
  return array.map(function(item){
    return Array.isArray(item) ? mapAll(item) : item * 3;
  });
}
alert(JSON.stringify(mapAll(arr)));

edited Jul 17, 2015 at 13:37

answered Jul 17, 2015 at 13:32

Joseph

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Oleksandr T. · Accepted Answer · 2015-07-17 13:47:53Z

2

Version with callback function where you can do with array elements what you want (el * 2 or something else)

var arr = [[1,2,3],[1,2,3],[[1,2],[1,2]],1,2,3];

function mapAll(array, cb) {
    for (var i = 0, len = array.length; i < len; i++) {
        if (Array.isArray(array[i])) {
            mapAll(array[i], cb);
        } else {        
            array[i] = cb(array[i]);
        }
    }
    
    return array;
};

var res = mapAll(arr, function (el) {
    return el * 3;
});

console.log(JSON.stringify(res));

edited Jul 17, 2015 at 13:47

answered Jul 17, 2015 at 13:38

Oleksandr T.

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