Cacher is the code snippet organizer for pro developers

var students = [
  {
    name: 'Peter',
    age: 19,
    score: 73,
    final: 83,
    school: 'La Sorbona'
  },
  {
    name: 'Julia',
    age: 22,
    score: 38,
    final: 83,
    school: 'St Louis'
  },
  {
    name: 'Rachel',
    age: 25,
    score: 99,
    final: 83,
    school: 'La Zarra'
  },
  {
    name: 'Charles',
    age: 18,
    score: 59,
    final: 83,
    school: 'St Louis'
  },
  {
    name: 'Anna',
    age: 27,
    score: 51,
    final: 83,
    school: 'La Sorbona'
  },
];

var defaults = {grade: 3, country: 'UK'};
var copy = _.clone(students[0]);

_.each(students, function(elem, index, list) {
    var avg = ( elem.score + elem.final ) / 2;
    _.extend(elem, {'average_score': avg});
   _.defaults(elem, defaults);
});

console.log(students);
console.log(copy);