How can I combine an array of objects with the same keys into one object?

Question

If I start with the following:

var people = [
   {id: 9, name: 'Bob', age: 14},
   {id: 11, name: 'Joe', age: 15},
   {id: 12, name: 'Ash', age: 24}]

What I am trying to get using underscore.js or lodash is a single hash/object with an array of all the values from the collection:

{
   id: [9, 11, 12],
   name: ['Bob', 'Joe', 'Ash'],
   age: [14, 15, 24]
}

Any thoughts?

Answer 1

An answer in straightforward JavaScript code (no libraries):

var result = {};
for (var i = 0; i < people.length; i++) {
    var item = people[i];
    for (var key in item) {
        if (!(key in result))
            result[key] = [];
        result[key].push(item[key]);
    }
}

Answer 2

Here's an alternate plain javascript answer. It's basically the same as Nayuki's but possibly a bit more expressive.

var obj = {};
people.forEach(function(person){
    for(prop in person) {
        obj[prop] = obj[prop] || [];
        obj[prop].push(person[prop]);
    }
});

Answer 3

I don't know javascript much. But one approach would be to create three arrays, let's say

var id = [];
var name = [];
var age = [];

Then loop through the people array

for(var i=0; i<people.length; i++){
  id.push(people[i].id);
  name.push(people[i].name);
  age.push(people[i].age);
}

Now you have three arrays with respective ids, names and ages

The last step would be to create your final object

var object = {
  id:id
  name:name
  age:age
};

Answer 4

using array.map():

var acc = {};
for (k in people[0]) {
    acc[k] = people.map(function (x) {
        return x[k]
    })
}

fiddle

this solution assumes that all the needed keys will be found in people[0] ...

---

EDIT:

this is a more extreme version that should catch the keys along the way:

 people.reduce(function (ac, item) {
    for (k in item) {
        if(!ac[k])
        ac[k] =[];
        ac[k].push(item[k])
        }
    return ac
}, {})

fiddle2

Answer 5

An alternative that uses Object.keys , Array.prototype.reduce and Array.prototype.map methods:

var res = Object.keys(people[0]).reduce(function(ret, key) {
     ret[key] = people.map(function(el) { return el[key]; });
     return ret;
}, {});