Create unique values from duplicates in Javascript array of objects

Question

I have an array of duplicated objects in Javascript. I want to create an array of unique objects by adding the index of occurrence of the individual value.

This is my initial data:

const array= [
  {name:"A"},
  {name:"A"},
  {name:"A"},
  {name:"B"},
  {name:"B"},
  {name:"C"},
  {name:"C"},
];

This is expected end result:

const array= [
  {name:"A-0"},
  {name:"A-1"},
  {name:"A-2"},
  {name:"B-0"},
  {name:"B-1"},
  {name:"C-0"},
  {name:"C-1"},
];

I feel like this should be fairly simple, but got stuck on it for a while. Can you please advise how I'd go about this? Also if possible, I need it efficient as the array can hold up to 1000 items.

---

EDIT: This is my solution, but I don't feel like it's very efficient.

const array = [
  { name: "A" },
  { name: "A" },
  { name: "C" },
  { name: "B" },
  { name: "A" },
  { name: "C" },
  { name: "B" },
];

const sortedArray = _.sortBy(array, 'name');

let previousItem = {
   name: '',
   counter: 0
};
const indexedArray = sortedArray.map((item) => {
  if (item.name === previousItem.name) {
    previousItem.counter += 1;
    const name = `${item.name}-${previousItem.counter}`;
    return { name };
  } else {
    previousItem = { name: item.name, counter: 0};
    return item;
  }
});

Answer 1

Currently you are sorting it first then looping over it, which may be not the most efficient solution.

I would suggest you to map over it with a helping object.

const a = [{name:"A"},{name:"A"},{name:"A"},{name:"B"},{name:"B"},{name:"C"},{name:"C"},], o = {};

const r = a.map(({ name }) => {
   typeof o[name] === 'number' ? o[name]++ : o[name] = 0;
   return { name: `${name}-${o[name]}` };
});
   
console.log(r);

Answer 2

Keep a counter, and if the current name changes, reset the counter.

This version mutates the objects. Not sure if you want a copy or not. You could potentially sort the array by object name first to ensure they are in order (if that's not already an existing precondition.)

const array = [
  { name: "A" },
  { name: "A" },
  { name: "A" },
  { name: "B" },
  { name: "B" },
  { name: "C" },
  { name: "C" },
];

let name, index;
for (let i in array) {
  index = array[i].name == name ? index + 1 : 0;
  name = array[i].name;
  array[i].name += `-${index}`;
}

console.log(array);

---

Another way, if you don't want to sort, and don't want to mutate any objects, is to use a map and keep track of the current index for each object.

const array = [
  // NOTE: I put the items in mixed up order.
  { name: "A" },
  { name: "C" },
  { name: "A" },
  { name: "B" },
  { name: "A" },
  { name: "C" },
  { name: "B" },
];

let index = {};
let next = name => index[name] = index[name] + 1 || 0;
let result = array.map(obj => ({ ...obj, name: obj.name + '-' + next(obj.name) }));
console.log(result);