Transform array of objects to another array of objects with unique id-s and array of names

Question

How to transform this items array to result array (objects should be with unique id and have key 'names' with array of name properties from objects with the same id):

Original array:

const items = [
{id: 1, name: 'a'}, 
{id: 2, name: 'b'}, 
{id: 3, name: 'c'}, 
{id: 1, name: 'd'}, 
{id: 3, name: 'f'}
];

Transformed array:

const result = [
{id: 1, names: ['a', 'd']}, 
{id: 2, names ['b']}, 
{id: 3, names: ['c', 'f']}
];

Answer 1

You can use Array.reduce to get the result.

const inputArray = [
  {id: 1, name: 'a'}, 
  {id: 2, name: 'b'}, 
  {id: 3, name: 'c'}, 
  {id: 1, name: 'd'}, 
  {id: 3, name: 'f'}
];

const result = inputArray.reduce((acc, item) => {
   const exist = acc.find(e => e.id == item.id);
   // check exist in result
   if (exist) {
      // exist: push 'name' value to 'names' array
      exist['names'].push(item.name);
   } else {
      // not exist: create new item in result
      acc.push({
         'id': item.id,
         'names': [item.name]
      });
   }
   
   return acc;
}, []);

console.log(result);