How can i convert Object keys to an array of elements that are number of times the key value in Javascript?

Question

e.g

obj = {a:2, b:3, c:1}

The transformed array is:

['a','a','b','b','b','c']

Answer 1

You can do it using reduce:

const obj = {a:2, b:3, c:1};

const res = Object.keys(obj).reduce((arr, key) => {
  return arr.concat( new Array(obj[key]).fill(key) );
}, []);

console.log(res); // ["a","a","b","b","b","c"]

Explanation:

• Object.keys() returns an array of all the keys: ["a", "b", "c"]

• We then loop over them with reduce, and while doing so, we build an array. For every key, we create a new array with the same length as the value, and fill it with the key (a, b...).

• We then concatenate them together with concat.

Answer 2

Get entries and take a flat map with an array of a wanted length and fill the array with the key.

const
    object = { a: 2, b: 3, c: 1 },
    result = Object
        .entries(object)
        .flatMap(([key, value]) => Array(value).fill(key));

console.log(result);

Answer 3

Try:

let obj = { a:2, b:3, c:1 }
let newObj = [];

for (var key in obj) {
  while (obj[key]) {
    newObj.push(key);
    obj[key]--;
  }
}

console.log(newObj);