Javascript: Count duplicates in an array, ES6

array_dupplicate_counter.js

// Scenario:
// You have a javascript array that likely has some duplicate values and you would like a count of those values.

const compressArray = arr => {
  const compressed = [];
  // make a copy of the input array
  const copy = arr.slice(0);
  // first loop goes over every element
  for (let i = 0; i < arr.length; i++) {
    let myCount = 0;
    // loop over every element in the copy and see if it's the same
    for (let w = 0; w < copy.length; w++) {
      if (arr[i] === copy[w]) {
        // increase amount of times duplicate is found
        myCount++;
        // sets item to undefined
        delete copy[w];
      }
    }
    if (myCount > 0) {
      const a = {};
      a.value = arr[i];
      a.count = myCount;
      compressed.push(a);
    }
  }
  return compressed;
};

const testArray = ['dog', 'dog', 'cat', 'buffalo', 'wolf', 'cat', 'tiger', 'cat'];;
console.log(compressArray(testArray));

// console output:
// [
//   { value: 'dog', count: 2 }, 
//   { value: 'cat', count: 3 }, 
//   { value: 'buffalo', count: 1 }, 
//   { value: 'wolf', count: 1 }, 
//   { value: 'tiger', count: 1 }
// ]

const sorted = compressArray(testArray).sort((a, b) => b.count - a.count);
console.log(sorted);

// console output:
// [
//   { value: 'cat', count: 3 }, 
//   { value: 'dog', count: 2 }, 
//   { value: 'buffalo', count: 1 }, 
//   { value: 'wolf', count: 1 }, 
//   { value: 'tiger', count: 1 }
// ]