gistfile1.txt

var people = [{
    name:"santiago",
    age:25,
    country:"españa"
},{
    name:"la",
    age:23,
    country:"colombia"
},{
    name:"juan",
    age:29,
    country:"colombia"
}]

people.reduce(function(sum, current){
     return sum + current.age
},0)

people.reduce(function(groupedByObject, current){
    let country = current.country;
      if(!groupedByObject[country])
      	 groupedByObject[country] = 0;
      groupedByObject[country] += current.age;
      return groupedByObject;
}, {})