Nodejs Array Group By groupBy(callback)

Method Source Code

// write a function on the Array prototype 
// called groupBy(callback) the takes a callback 
// function. For each item in groupBy, callback's 
// arguments will be (value, index, array).
// //from   w w  w . j  a v a2s .  c o m
// The value returned by the callback becomes the 
// key for the original value in a new collection.
// 
// i.e. 
// 
// [1,2,3,4,5,6,7,8,9,10].groupBy(function(v, i, arr){
//      return (v%2 === 0) ? 'even' : 'odd'
// })
// 
// //--> { odd: [1,3,5,7,9], even: [2,4,6,8,10] }

Array.prototype.groupBy = function(callback){
    this.reduce() 
   // ['1', '3', '5', '7', '9'].groupBy(() => 'odd')
   // ['2', '4', '6', '8'].groupBy(() => 'even')
var result{}
this.forEach(v, i, arr) = function(){}

}


v, i, arr

Array.prototype.groupBy = function(callback){ 

   var evens = Array.groupBy.forEach([9])

   if(Array.groupBy %2 === 0){
      return even[]
   }else{ return odd[]}

Related

1. groupBy(callback)

   Array.prototype.groupBy = function(callback) {
       let obj = {}
       this.forEach(el => {
           let index = callback(el)
           if (!obj.hasOwnProperty(index)) {
               obj[index] = []
           obj[index].push(el)
       })
   ...
   

2. groupBy(callback)

   Array.prototype.groupBy = function(callback){
   var results = {};
     this.forEach(function (el){
       var key = callback(el);
       if (key in results === false) {
         results[key] = [];
       results[key].push(el);
    });
   ...
   

3. groupBy(fieldName)

   Array.prototype.groupBy = function (fieldName) {
       if (this.some(item => item.hasOwnProperty(fieldName))) {
           let uniqVal = this.map(item => item[fieldName]).filter((value, item, array) => array.indexOf(value) === item);
           let tempObj = {};
           uniqVal.map(item => tempObj[item] = []);
           this.forEach(item => {
               for (let name in tempObj) {
                   if (item[fieldName] == name) {
                       tempObj[name].push(item);
   ...
   

4. groupBy(fieldkey,fieldsums,fn)

   Array.prototype.groupBy=function(fieldkey,fieldsums,fn){
     var groups = _.groupBy(this,function(item){
       return item[fieldkey];
     });
     async.map(_.keys(groups)
       ,function(key,callback){
         var value = groups[key];
         var r = {};
         r[fieldkey] = key;
   ...
   

5. 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])] = [
   ...
   

6. 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
     }, {})
   ...