Sorting rows by values of row property that is array with mfDefaultSorter

[iDGE90]

Is there a way to sort orders by the sum of the items quantity (without changing the structure of the orders array):

const orders = [
  {
    id: 1,
    title: 'Order 1'
    items: [
      {quantity: 20},
      {quantity: 30},
      {quantity: 40},
    ]
  },
  {
    id: 2,
    title: 'Order 2'
    items: [
      {quantity: 50},
      {quantity: 10},
    ]
  }
];

<mfDefaultSorter [by]="?????">Quantity</mfDefaultSorter>

[iDGE90]

If any one needs solution https://stackoverflow.com/questions/51983303/angular-2-angular2-datatable-sorting-rows-by-values-of-row-property-that-is/51983457#51983457