Nodejs Array Reduce reduce(combiner, initialValue)

Method Source Code

// Exercise 16: Implement reduce()

// Let's add a reduce() function to the Array type. Like map

// [1,2,3].reduce(function(accumulatedValue, currentValue) { return accumulatedValue + currentValue; }); === [6];
// [1,2,3].reduce(function(accumulatedValue, currentValue) { return accumulatedValue + currentValue; }, 10); === [16];

Array.prototype.reduce = function (combiner, initialValue) {
  var counter,/*from  w ww. jav  a 2s  .c  o  m*/
    accumulatedValue;

  // If the array is empty, do nothing
  if (this.length === 0) {
    return this;
  }

  // If the user didn't pass an initial value, use the first item.
  if (arguments.length === 1) {
    counter = 1;
    accumulatedValue = this[0];
  } else if (arguments.length >= 2) {
    counter = 0;
    accumulatedValue = initialValue;
  } else {
    throw "Invalid arguments.";
  }

  // Loop through the array, feeding the current value and the result of
  // the previous computation back into the combiner function until
  // we've exhausted the entire array and are left with only one value.
  while (counter < this.length) {
    accumulatedValue = combiner(accumulatedValue, this[counter]);
    counter++;
  }

  return [accumulatedValue];
};

Related

1. reduce(callback, memo)

   Array.prototype.reduce = function (callback, memo) {
       var obj = this;
       var value, accumulated_value = 0;
       for (var i = 0; i < obj.length; i++) {
           value = obj[i];
           accumulated_value = callback.call(null, accumulated_value, value);
       return accumulated_value;
   };
   ...
   

2. reduce(cb, res)

   Array.prototype.reduce = function(cb, res){
       var arr = Object(this);
       for(var i=0;i<arr.length;i++){
           res = cb.call(res, arr[i], i);
       return res;
   

3. reduce(combiner, initialValue)

   Array.prototype.reduce = function (combiner, initialValue) {
     var counter,
       accumulatedValue;
     if (this.length === 0) {
       return this;
     else {
       if (arguments.length === 1) {
         counter = 1;
   ...
   

4. reduce(combiner, initialValue)

   Array.prototype.reduce = function(combiner, initialValue) {
     var counter,
       accValue;
     if (this.length === 0) {
       return this;
     else {
       if (arguments.length === 1) {
         counter = 1;
   ...
   

5. reduce(combiner, initialValue)

   Array.prototype.reduce = function(combiner, initialValue) {
     var counter,
       accumulatedValue;
     if (this.length === 0) {
       return this;
     else {
       if (arguments.length === 1) {
         counter = 1;
   ...
   

6. reduce(combiner, initialValue)

   Array.prototype.reduce = function(combiner, initialValue) {
     var counter,
       accumulatedValue;
     if (this.length === 1) {
       return this;
     } else {
         if (arguments.length === 1) {
           counter = 1;
           accumulatedValue = this[0];
   ...
   

7. reduce(f, firstValue)

   Array.prototype.reduce = function(f, firstValue){
      var value = firstValue;
      for (var i =0; i<this.length; i++){
         value = f(this[i], value);
      return value;
   };
   [1,2,3].reduce(function(currentValue ,value){return value+=currentValue;}, 0);
   [1,2,3].reduce(function(currentValue ,value){return value*=currentValue;}, 0);
   ...
   

8. reduce(f, inital)

   var arr = [0,1,2,3,4];
   var sum = function(x, y) { return x + y; };
   Array.prototype.reduce = function(f, inital) {
       var acc = initial;
       for (var i = 0; i < this.length; i++) {
           acc = f(acc, this[i]);
       return acc;
   };
   ...
   

9. reduce(f, initial)

   var arr = [0,1,2,3,4];
   var sum = function(total, newValue) { return total + newValue; };
   Array.prototype.reduce = function(f, initial) {
       var acc = initial;
       for (var i = 0; i < this.length; i++) {
           acc = f(acc, this[i]);
       return acc;
   };
   ...