mean_median_mode.js

const getMedian = arr => {
  const arrLen = arr.length

  if (arrLen % 2 !== 0) {
    return arr[Math.floor(arrLen / 2)]
  } else {
    const m1 = arr[(arrLen / 2) - 1]
    const m2 = arr[arrLen / 2]
    return (m1 + m2) / 2
  }
}

const getModes = hash => {
  let modes = []
  let maxFrequency = 0

  for(let number in hash) {
    const currentFreq = hash[number]

    if (currentFreq > maxFrequency) {
      modes = [number]
      maxFrequency = currentFreq
    } else if (currentFreq === maxFrequency) {
      modes.push(number)
    }
  }

  if (modes.length === Object.keys(hash).length) modes = []
  
  return modes
}

const meanMedianMode = arr => {
  arr.sort( (a,b) => a - b )
  
  let sum = 0
  let hash = {}

  for(let idx in arr) {
    const num = arr[idx]
    sum += num

    if (!hash[num]) hash[num] = 0
    hash[num]++
  }

  return {
    mean: sum / arr.length, 
    median: getMedian(arr),
    modes: getModes(hash)
  }
}

const arr = [1,2,3,4,5,4,6,1] // 3.25, 3.5, [1,4]
const arr2 = [9,10,23,10,23,9] // 14, 10, []
const result = meanMedianMode(arr)
const result2 = meanMedianMode(arr2)
console.log(result)
console.log(result2)