Nodejs Array Group By groupBy(prop)

Method Source Code

Array.prototype.groupBy = function(prop) {
  return this.reduce(function(groups, item) {
    var val = item[prop];
    groups[val] = groups[val] || [];/*from  w  w  w  .  j  a  v  a2 s . c  o  m*/
    groups[val].push(item);
    return groups;
  }, {});
}

let students = [
  { name: "Jane", module: "4FE", track: "frontEnd" },
  { name: "Jane", module: "3FE", track: "frontEnd" },
  { name: "Jane", module: "3BE", track: "backEnd" },
  { name: "Jane", module: "4FE", track: "frontEnd" },
  { name: "Jane", module: "2BE", track: "backEnd" },
  { name: "Jane", module: "3BE", track: "backEnd" }
];

console.log(students.groupBy('track'))

Related

1. groupBy(fn)

   Array.prototype.groupBy = function (fn) {
     var result = {
     };
     for (var i = 0; i < this.length; i++)
       try {
         if (!result[fn(this[i])])
           result[fn(this[i])] = [
   ...
   

2. groupBy(fn)

   Array.prototype.groupBy = function(fn) {
     if (!fn) return this.groupBy(x => x)
     return this.reduce((acc, x) => {
       if (acc[fn(x)]) return acc
       acc[fn(x)] = this.filter(i => {
         return fn(x) === fn(i)
       })
       return acc
     }, {})
   ...
   

3. groupBy(funcProp)

   Array.prototype.groupBy = function (funcProp) {
     return this.reduce(function (accumulator, value) {
       (accumulator[funcProp(value)] = accumulator[funcProp(value)] || []).push(value);
       return accumulator;
     }, {});
   };
   Array.prototype.orderBy = function (funcProp, desc = false) {
     return this.sort((a, b) => {
       var aValue = funcProp(a);
   ...
   

4. groupBy(groupFunction)

   function groupByArray(array, groupFunction) {
       var map = {}
       array.forEach(
       function forEachFunction(item, index, array) {
           var groupName = groupFunction(item, index, array)
           if (map[groupName]) map[groupName].push(item)
           else map[groupName] = [item]
       })
       return map
   ...
   

5. groupBy(hash)

   Array.prototype.groupBy = function(hash){
     var _hash = hash ? hash : function(o){return o;};
     var _map = {};
     var put = function(map, key, value){
       if (!map[_hash(key)]) {
           map[_hash(key)] = {};
           map[_hash(key)].group = [];
           map[_hash(key)].key = key;
       map[_hash(key)].group.push(value); 
     this.map(function(obj){
       put(_map, obj, obj);
     });
     return Object.keys(_map).map(function(key){
       return {key: _map[key].key, group: _map[key].group};
     });
   

6. groupBy(selector, comparer)

   Array.prototype.groupBy = function (selector, comparer) {
       var grp = [];
       var l = this.length;
       comparer = comparer || EqualityComparer;
       selector = selector || Selector;
       for (var i = 0; i < l; i++) {
           var k = selector(this[i]);
           var g = grp.first(function (u) { return comparer(u.key, k); });
           if (!g) {
   ...