Calculate all possible combinations of r elements in a given array of size n

calculateCombination.js

const calculateCombination = (arr, r) => {
  const data = [];
  combinationUtil(arr, data, 0, arr.length - 1, 0, r);
  return calculate(result);
};

const combinationUtil = (arr, data, start, end, index, r) => {
  if (index == r) {
    for (let j = 0; j < r; j++) {
      result.push(data[j]);
    }
  }

  let i = start;
  while (i <= end && end - i + 1 >= r - index) {
    data[index] = arr[i];
    combinationUtil(arr, data, i + 1, end, index + 1, r);
    i += 1;
  }
};

const calculate = (array) => {
  let sumAbs = 0;
  let divider = 0;
  for (let i = 0; i < array.length; i += 2) {
    sumAbs += Math.abs(array[i] - array[i + 1]);
    divider++;
  }
  return sumAbs / divider;
};

const arr = [1, 2, 3, 4];
const r = 2;
const result = [];

calculateCombination(arr, r);