3m.js

/*-----------------------------------------------------------------------------
1.3 function used to calculate: mean, median, mode.
2.writing another function to package them.
3.MODE: if there is no number repeated, return false.
3.MODE: maybe there is not only one mode.

the reference is from UdemyCourse: LearningAlgorithmsInJavascriptFromScratch
-----------------------------------------------------------------------------*/

function meanMedianMode(arr) {
  return {
    mean: getMean(arr),
    median: getMedian(arr),
    mode: getMode(arr),
  };
}


meanMedianMode([1, 4, 21, 23, 24, 32, 33, 43]);
 

getMean.js

function getMean(arr) {
  return (
    arr.reduce((a, b) => {
      return a + b;
    }) / arr.length
  );
}

getMedian.js

function getMedian(arr) {
  // sorting in order
  // if only using sort() default, 1000 may ordered first but not 40 
  arr = arr.sort((a, b) => {
    return a - b;
  });

  if (arr.length % 2 === 0)
    return (arr[arr.length / 2 - 1] + arr[arr.length / 2]) / 2;
  else {
    return arr[(arr.length - 1) / 2];
  }
}

getMode.js

function getMode(arr) {
  // create a dict
  var countObj = {};
  arr.forEach(n => {
    if (!countObj[n]) {
      countObj[n] = 0;
    }
    countObj[n]++;
  });

  var modes = [];
  var maxFrequency = 0;

  // iterate it to find the max frequency
  for (var n in countObj) {
    if (countObj[n] > maxFrequency) {
      modes = [n];
      maxFrequency = countObj[n];
    } else if (countObj[n] === maxFrequency) {
      modes.push(n);
    }
  }
  
  // every element is mode means no mode.
  if (modes.length === Object.keys(countObj).length) {
    modes = false;
  }
  
  return modes;
}