Create array based on object properties

Question

I'd like to use an object to configure some settings for an app. My idea is to start with this:

var obj = {
    property_one: 3;
    property_two: 2;
    property_three: 1;
}

And I would like to end up with this:

var array = [
    'property_one','property_one','property_one',
    'property_two','property_two',
    'property_three'
]

My current solution is to do this for each property:

function theConstructor(){
    for(i=1; i <= obj.property_one; i++){
        this.array.push('property_one');
    };
    for(i=1; i <= obj.property_two; i++){
        this.array.push('property_two');
    };
    for(i=1; i <= obj.property_two; i++){
        this.array.push('property_two');
    };
}

But this gets tedious, because I might have many properties, and these might change as the app evolves.

I know I can loop through object's properties like this:

for (var key in obj) {
  if (obj.hasOwnProperty(key)) {
    array.push(key);
  }
}

But this will push the value to the array, not the key (as a string). Any ideas about how I can do this more efficiently?

Viktor Kukurba · Accepted Answer · 2016-02-28 12:18:03Z

2

Try this

function theConstructor(){
  for (var key in obj) {
    if (obj.hasOwnProperty(key)) {
      for(var i=1; i <= obj[key]; i++){
        this.array.push(key);
      };
    }
  }
}

edited Feb 28, 2016 at 12:18

answered Feb 28, 2016 at 12:10

Viktor Kukurba

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2 Comments

FreeLightman Over a year ago

You missed to declare variable i.

Joey M-H Over a year ago

Thanks a lot, don't know how I didn't see this looking back!

Dmitri Pavlutin · Accepted Answer · 2016-02-28 12:36:15Z

1

Using Array.prototype.reduce():

var obj = {
  property_one: 3,
  property_two: 2,
  property_three: 1
};

var resultArray = Object.keys(obj).reduce(function(result, curItem) {
  for (var index = 0; index < obj[curItem]; index++) {
    result.push(curItem);
  }
  return result;
}, []);

document.write(JSON.stringify(resultArray));

edited Feb 28, 2016 at 12:36

answered Feb 28, 2016 at 12:30

Dmitri Pavlutin

19.3k8 gold badges41 silver badges46 bronze badges

1 Comment

Joey M-H Over a year ago

Thanks, this is a very elegant solution.

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