Nodejs Array Reduce reduce(combiner, initialValue)

Method Source Code

// This implementation of the reduce function is copied from ReactiveX.io
// for self-learning and practicing application. 

Array.prototype.reduce = function(combiner, initialValue) {
  var counter,//  ww w . j  ava2s . com
    accumulatedValue;

  if (this.length === 1) {
    return this;
  } else {
      if (arguments.length === 1) {
        counter = 1;
        accumulatedValue = this[0];
      } else if (arguments >= 2) {
        counter = 0;
        accumulatedValue = initialValue;
      } else {
      throw "Invalid arguments.";
      }

      while (counter < this.length) {
        accumulatedValue = combiner(accumulatedValue, this[counter]);
        counter++;
      }

    return [accumulatedValue];
  }
}

var ratings = [2,1,5,3,4];

ratings.reduce(function(prev, curr) {
  if (curr > prev) {
    return prev = curr;
  } else {
    return prev;
  }
});

// My original written version adapted from Eloquent JavaScript:

function reduce(array, combine, start) {
  array.each(function(item) {
    start = combine(start, item);
  });
  return start;
}

Array.prototype.each = function(collection, callback) {
  var i, len, key;
  if (Array.isArray(collection)) {
    for (i = 0, len = collection.length; i < len; i += 1) {
      callback(collection[i]);
    } 
  } else {
    for (key in collection) {
      callback(collection[key]);
    }
  }
};

Related

1. 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;
   

2. 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;
   ...
   

3. 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;
   ...
   

4. 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;
   ...
   

5. reduce(combiner, initialValue)

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

6. 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);
   ...
   

7. 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;
   };
   ...
   

8. 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;
   };
   ...
   

9. reduce(f, value)

   Array.prototype.reduce = function (f, value) { 
       for (var i = 0; i < this.length; i++) { 
           value = f(this[i], value)
       return value