Loop Over Array of Objects and Combine them if they have similar keys

Question

I am trying to iterate over an array that's similar to the below structure, and for each object that has the same id, I want them combined into a single object but with an array of all the 'names' associated with that id. My Array is pre-sorted by id and I can't use JQuery, only vanilla JS.

Convert this:

var array = [
   {id=1, name = "Orange"},
   {id=1, name = "Blue"},
   {id=1, name = "Green"},
   {id=2, name = "Blue"},
   {id=3, name = "Orange"},
   {id=3, name = "Blue"}
]

To this:

var newArray = [
   {id=1, nameList = [Orange, Blue, Green]},
   {id=2, nameList = [Blue]},
   {id=3, namelist = [Orange, Blue]}
]

I was trying to do something like this by comparing the first object to the next object in the array, then setting the first object to the second object, but got stuck because 'secondObject' wasn't actually the next object in the array.

for (var i in array) {
   firstObject = array[i];
   secondObject = array[i + 1];
   if (firstObject.id === secondObject.id) {
      firstObject['nameList'] = [firstObject.name + ',' + secondObject.name]

    } else {
    continue;
    }
  firstObject = secondObject;


}

I have to do this with a couple thousand id's, and most of the id's are repeated with different names, but there are a few single id objects like id 2.

Answer 1

An alternative is using the function reduce

var array = [   {id:1, name : "Orange"},   {id:1, name : "Blue"},   {id:1, name : "Green"},   {id:2, name : "Blue"},   {id:3, name : "Orange"},   {id:3, name : "Blue"}]

var result = Object.values(array.reduce((a, c) => {
  (a[c.id] || (a[c.id] = {id: c.id, nameList: []})).nameList.push(c.name);
  return a;
}, {}));

console.log(result);

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