Nodejs Array Flatten flatten()

Method Source Code

/********************************************************************************
 * Eloquent JavaScript, Ch. 5 - Flattening:
 *
 * Use the reduce method in combination with the concat method to ?flatten? an 
 * array of arrays into a single array that has all the elements of the input 
 * arrays.//from   ww w.j av  a  2s.  c  om
 ********************************************************************************/

var arrays = [[1, 2, 3], [4, 5], [6]];

// simple use case:
console.log(arrays.reduce(function(a, b){
   return a.concat(b);
}));
// ? [1, 2, 3, 4, 5, 6]


// When called on an array of any depth, returns a *new*, completely flat array;
//
// This is accomplished by progressively 'reducing' the elements in the array.
// Given a value 'a', where 'a' contains all previously reduced elements, and
// a value 'b', which holds the next element to be reduced:
//
//   1) if either 'a' or 'b' are arrays, flatten them; 
//
//   2) if 'a' is not an array, convert it to an array placing its original value
//      inside;
// 
//   3) concatenate 'b' to 'a', and proceed reduction with the result, and next
//      element in the array;
Array.prototype.flatten = function(){
   return this.reduce(function(a, b){
      if(!Array.prototype.isPrototypeOf(a))
         a = [a];
      else
         a = a.flatten();
      if(Array.prototype.isPrototypeOf(b))
         b = b.flatten();

      return a.concat(b);
   });
};


// using flatten method of Array prototype:
arrays.push([[7, 8, 9], [10, [11, [12], null, undefined, NaN, Infinity]]]);
console.log(arrays.flatten());
// ? [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, null, undefined, NaN, Infinity]

// test for 'arrays' integrity:
console.log(arrays);

Related

1. flatten()

   Array.prototype.flatten = function () {
     var toReturn = [];
     for (var i = 0, len = this.length; i < len; i++) {
       if (this[i] instanceof Array) {
         toReturn = toReturn.concat(this[i].flatten());
       } else {
         toReturn.push(this[i]);
     return toReturn;
   };
   

2. flatten()

   Array.prototype.flatten = function() {
     return this.reduce(function(a,b) {
       return a.concat(b)
     }, [])
   

3. flatten()

   Array.prototype.flatten = function(){
       var flattenArray = [];
       for (var el in this) {
           var currElement = this[el];
           if (Object.prototype.toString.call(currElement) === '[object Array]' ) {
               for (var i in currElement) {
                   flattenArray.push(currElement[i]);
           } else {
   ...
   

4. flatten()

   var slice = Array.prototype.slice;
   Array.prototype.flatten = function () {
     var obj, result = [];
     for (var i = 0, l = this.length; i < l; ++i ) {
       obj = this[ i ];
       if ( Array.isArray( obj ) ) {
         result = result.concat( obj.flatten() );
       } else {
         result[ result.length ] = obj;
   ...
   

5. flatten()

   Array.prototype.flatten = Array.prototype.flatten || function() {
     'use strict';
     var that = this;
     for (var i = 0; i < that.length; i += 1) {
       if (Array.isArray(that[i])) {
         that = that.concat.apply([], that);
         i -= 1;
     return that;
   };
   Array.prototype.flatten1 = Array.prototype.flatten1 || function() {
     'use strict';
     var res = [];
     (function flatten(arr) {
       for (var i = 0; i < arr.length; i += 1) {
         if (Array.isArray(arr[i])) {
           flatten(arr[i]);
         } else {
           res.push(arr[i]);
     }(this));
     return res;
   };
   Array.prototype.flatten2 = Array.prototype.flatten2 || function() {
     'use strict';
     for (var i = 0; i < this.length; i += 1) {
       if (Array.isArray(this[i])) {
         this.splice.apply(this, [i, 1].concat(this[i].flatten()));
     return this;
   };
   var a = [1, 2, [3, 4, [5, 6]]];
   console.log(a.flatten()); 
   console.log(a); 
   console.log(a.flatten1()); 
   console.log(a); 
   console.log(a.flatten2()); 
   console.log(a); 
   

6. flatten(array)

   Array.prototype.flatten = function(array) {
     return this.reduce((prev, next) => prev.concat(next), []);
   };
   

7. flatten(func)

   Array.prototype.flatten = function (func) {
     var result = [];
     forEach(this, function (element) {
       forEach(func(element), function (child) {
         result.push(child);
       });
     });
     return result;  
   

8. flatten(nil)

   Array.prototype.flatten = function(nil){
       result = new Array();
       for(var i = 0; i < this.length; i++){
     item = this[i];
     if($.isArray(item)) for(var j = 0; j < item.length; j++) result.push(item[j]);
     else result.push(item);
       return result;
   };
   ...
   

9. flatten(prevous)

   Array.prototype.flatten = function(prevous) {
     var flattenedArr = prevous || [];
     for (var i = 0; i < this.length; i++) {
       if(Array.isArray(this[i])) {
         this[i].flatten(flattenedArr);
       } else if(this[i] === null) {
       } else {
         flattenedArr.push(this[i]);
     return flattenedArr;