Javascript, repeating an object key N-times, being N its value

Question

I was wondering how to do this in the more cleaner and optimal way:

I have an Object with the following structure:

{
   \"125\": 2,
   \"439\": 3,
           


        

Answer 1

A helper function:

function flatten(obj){
 //static Array method: create array (a elements, value b) 
 Array.aXb = Array.aXb || function(a,b){
    b = b || 0;
    return String(this(a)).split(',').map(function(){return b;});
 }
 //obj2array 
 var arr = [];
 for (var k in obj)
    if (+obj[k]) arr = arr.concat(Array.aXb(+obj[k],k));
 return arr;
}
var obj= {"125": 2,"439": 3,
          "560": 1,"999": 2 },
flatten(obj); //=> [125,125,439,439,439,560,999,999]

Answer 2

Whether any of these approaches is cleaner is quite subjective:

// some helper function for creating an array with repeated values
function repeat(val, times) {
    var arr = [];
    for(var i = 0; i < times; i = arr.push(val));
    return arr;
}

function convert(obj) {
    var result = [], key;
    for(key in obj) {
        result = result.concat(repeat(+key, obj[key]));
    }
    return result;
}

Or a more functional approach:

Object.keys(obj).reduce(function(result, key) {
    return result.concat(repeat(+key, obj[key]));
}, []);

// with underscore.js
_.reduce(_.keys(obj), function(result, key) {
    return result.concat(repeat(+key, obj[key]));
}, []);

Answer 3

Try this:

var obj = {
  "125": 2,
  "439": 3,
  "560": 1,
  "999": 2
}

var arr = [];

for (prop in obj) {
  for (var i = 0; i < obj[prop]; i++)
    arr.push(parseInt(prop));
}

console.log(arr)

Answer 4

I know this is plain JavaScript but seems cleaner to me than the code you posted:

var dict = {
   "125": 2,
   "439": 3,
   "560": 1,
   "999": 2
}
var result = [];

for(key in dict)
    for(i = 0; i < dict[key]; i++)
        result.push(key * 1);

alert(result);

Answer 5

The problem with the other answers above is that the for..in language construct in javascript is going to involve all keys from the objects prototype chain. In this case, we should check and add only the correct keys.

var obj= {
   "125": 2,
   "439": 3,
   "560": 1,
   "999": 2
}

var arr=[];

for (var item in map) {
  //important check!
  if (map.hasOwnProperty(item)) {
    arr.push(item);
  }
}

Also see: http://www.yuiblog.com/blog/2006/09/26/for-in-intrigue/

Answer 6

Hmm... not sure if I got at, but maybe something like this:

var myObj = {
   "125": 2,
   "439": 3,
   "560": 1,
   "999": 2
},
myArray = [];

for(k in myObj){
    for(i = 0; i < myObj[k]; i++){
        myArray.push(k);
    }
}
console.log(myArray)