Mean, Median & Mode functions using JavaScript

mean-median-mode-math.js

/**
 * An average of a set of numbers.
 * @param {number[]} values 
 * @returns {number}
 */
 export function mean(...values) {
  if (values.length === 0) return;
  return values.reduce((a, b) => a + b, 0) / values.length;
}

/**
 * A middle number of a set numbers. 
 * e.g. [1, 2, 3], median = 2
 * e.g. [1, 2, 3, 4], median = mean(2, 3) = 2.5
 * @param {number[]} values 
 * @returns {number}
 */
export function median(...values) {
  const l = values.length;
  if (l === 0) return;
  values = values.sort();

  if (l % 2 === 0) {
    return mean(values[(l / 2) - 1], values[(l / 2)])
  } else {
    return values[(l - 1) / 2];
  }
}

/**
 * Find most occurring numbers.
 * e.g. [1, 2, 3, 4, 3], mode = 3 
 * e.g. [1, 1, 2, 2, 3, 4], mode = [1, 2]
 * e.g. [1, 2, 3], mode = undefined
 * @param {number[]} values 
 * @returns {number[]}
 */
export function mode(...values) {
  const l = values.length;
  if (l === 0) return;

  const map = new Map();
  let sum = 0;

  for (const value of values) {

    if (map.has(value)) {
      map.set(value, map.get(value) + 1);
      continue;
    }

    sum++;
    map.set(value, 1);
  }

  // no-mode
  if (sum === l) {
    return [];
  }

  let maxCount = 0;
  let modes = [];

  for (const [number, count] of map.entries()) {

    if (count > maxCount) {
      maxCount = count;
      modes = [number];
      continue;
    }

    if (count === maxCount) {
      modes = [
        ...modes,
        number,
      ];
    }
  }

  return modes
}

console.log('mean:', mean(1, 2, 3, 4, 5))
console.log('median:', median(1, 2, 3, 4, 5))
console.log('mode:', mode(1, 2, 3, 4, 5, 6, 7, 8, 1, 2))

// => mean: 3
// => median: 3
// => mode: [ 1, 2 ]