How to count the number of occurances in an array and translate it into an array of object?-CodePudding

I am trying to take in an array of names (with duplicates) and output a array of objects.

Input: single array

const arr = ['M', 'M', 'M', 'S', 'S', 'S', 'R', 'C', 'S', 'S', 'S']

Output: array of objects

[
  {
    name: 'M'
    duplicates: 3
  },
  {
    name: 'S'
    duplicates: 6
  }...
]

I have tried this solution, but this is giving me the name of each array item for the key name. That is not what I want.

This is my current code:

const result = arr.reduce((acc, curr) => {
    acc[curr] ??
        (acc[curr] = {
            [curr]: 0,
        })
    acc[curr][curr]  
    return acc
}, [])
console.log(result)

/*output:
[
  C: {C: 1}
  M: {M: 3}
  R: {R: 1}
  S: {S: 6}
]
*/

CodePudding user response：

Index the accumulator by the element, increment counts for matching keys, strip out the index (with Object.values) at the end...

const arr = ['M', 'M', 'M', 'S', 'S', 'S', 'R', 'C', 'S', 'S', 'S'];

let result = Object.values(arr.reduce((acc, el) => {
  if (!acc.hasOwnProperty(el)) acc[el] = { name: el, duplicates: 0 };
  acc[el].duplicates  ;
  return acc;
}, {}));


console.log(result)