split array of objects into three seperate array based on a property

Question

I have a array of objects with property of id and size. Sum of objects size equals to 78 and I want to split this objects by three array. But I want to split possibly equal sum of size (~ 78/3 +-).

I have a this array of objects,

[
 {'id': '1', 'size': '10'},
 {'id': '2', 'size': '4'},
 {'id': '3', 'size': '6'},
 {'id': '4', 'size': '21'},
 {'id': '5', 'size': '2'},
 {'id': '6', 'size': '1'},
 {'id': '7', 'size': '6'},
 {'id': '8', 'size': '7'},
 {'id': '9', 'size': '8'},
 {'id': '1', 'size': '13'}
]

And I want

[
 [
  {'id': '4', 'size': '21'},
  {'id': '2', 'size': '4'}, 
  {'id': '6', 'size': '1'},
 ],
 [
  {'id': '1', 'size': '13'},
  {'id': '1', 'size': '10'},
  {'id': '5', 'size': '2'},
 ],
 [
  {'id': '3', 'size': '6'}, 
  {'id': '9', 'size': '8'},
  {'id': '7', 'size': '6'},
  {'id': '8', 'size': '7'},
 ]
]

Answer 1

This is an NP-complete problem so there is more then one solution. One approach I thought of is putting the bigger items first and then putting the smaller items where you have more space.

let items = [
    {'id': '1', 'size': 10},
    {'id': '2', 'size': 4},
    {'id': '3', 'size': 6},
    {'id': '4', 'size': 21},
    {'id': '5', 'size': 2},
    {'id': '6', 'size': 1},
    {'id': '7', 'size': 6},
    {'id': '8', 'size': 7},
    {'id': '9', 'size': 8},
    {'id': '1', 'size': 13}
];
//sort the array by size in reverse order
items.sort((a, b)=> b.size - a.size);
//array of sums
let sums = [0,0,0];
//final array of 3 arrays
let arrays = [[],[],[]];
for (let item of items) {
    //get index of the smallest sum
    let index =  sums.indexOf(Math.min.apply(null,sums));
    //add current item size to corresponding sum
    sums[index] += item.size;
    //add item to corresponding array
    arrays[index].push(item);
}
console.log(arrays);
console.log(sums);