Remove duplicates from array, convert to array of objects and add duplicate count property

Question

I have an array of strings:

var array = ['bob', 'charlie', 'bob', 'bob']; 

that I want to remove duplicates from, and then I'd like to convert it to an array of objects whilst adding a duplicate count property.

This is what I want to achieve:

var filteredData = [{ name: 'bob', count: 3}, { name: 'charlie', count: 1}];

How can I do that?

Answer 1

Ecmascript5 solution using Array.prototype.reduce() function:

var arr = ['bob', 'charlie', 'bob', 'bob'],
    counts = arr.reduce(function(r,s){
        (!r[s])? r[s] = {name: s, count: 1} : r[s]['count']+=1;
        return r;
    }, {}),
    result = Object.keys(counts).map(function(k){ return counts[k]; });
    
console.log(result);

---

Ecmascript6 version (with Object.values() function):

var arr = ['bob', 'charlie', 'bob', 'bob'],
    result = Object.values(arr.reduce((r,s) => {
        (!r[s])? r[s] = {name: s, count: 1} : r[s]['count']+=1;
        return r;
    }, {}));
    
console.log(result);

Answer 2

Using Map with Array#reduce:

const array = ['bob', 'charlie', 'bob', 'bob']; 

const result = [...array.reduce((map, name) => {
  const current = map.get(name) || { name, count: 0 };
  
  current.count++;

  return map.set(name, current);
}, new Map()).values()];

console.log(result);

Answer 3

Here is some straightforward usage of Array.prototype.reduce:

const data = ['bob', 'charlie', 'bob', 'bob']

const result = data.reduce(function(prev, curr) {
  const index = prev.findIndex(el => el.name === curr)

  if (index !== -1) {
    prev[index].count += 1
  } else {
    prev.push({ name: curr, count: 1 })
  }

  return prev
}, [])

console.log(result)