Get the element with the highest occurrence in an array

Question

I\'m looking for an elegant way of determining which element has the highest occurrence (mode) in a JavaScript array.

For example, in

[\'pear\', \'a         


        

Answer 1

As per George Jempty's request to have the algorithm account for ties, I propose a modified version of Matthew Flaschen's algorithm.

function modeString(array) {
  if (array.length == 0) return null;

  var modeMap = {},
    maxEl = array[0],
    maxCount = 1;

  for (var i = 0; i < array.length; i++) {
    var el = array[i];

    if (modeMap[el] == null) modeMap[el] = 1;
    else modeMap[el]++;

    if (modeMap[el] > maxCount) {
      maxEl = el;
      maxCount = modeMap[el];
    } else if (modeMap[el] == maxCount) {
      maxEl += "&" + el;
      maxCount = modeMap[el];
    }
  }
  return maxEl;
}

This will now return a string with the mode element(s) delimited by a & symbol. When the result is received it can be split on that & element and you have your mode(s).

Another option would be to return an array of mode element(s) like so:

function modeArray(array) {
  if (array.length == 0) return null;
  var modeMap = {},
    maxCount = 1,
    modes = [];

  for (var i = 0; i < array.length; i++) {
    var el = array[i];

    if (modeMap[el] == null) modeMap[el] = 1;
    else modeMap[el]++;

    if (modeMap[el] > maxCount) {
      modes = [el];
      maxCount = modeMap[el];
    } else if (modeMap[el] == maxCount) {
      modes.push(el);
      maxCount = modeMap[el];
    }
  }
  return modes;
}

In the above example you would then be able to handle the result of the function as an array of modes.