Javascript custom array prototype

Question

I have for example this multidimensional array:

MyArray[('A', 40, true), ('B', 20, false), ('C', 55, true), ('D', 17, true)]

and I'd like to implement a custom min() and max() prototype to get min and max only of thoses are 'true'... any trick? I'm stuck at it since I was thinking around .map() to extract a certain property but how to check if enabled to extract due of true/false property.

---

Precisely, I did:

var MyArray = [];
MyArray.push( {
 name: 'A',
 valueA: 40,
 valueB: 36,
 enabled: true
});
MyArray.push( {
 name: 'B',
 valueA: 20,
 valueB: 18,
 enabled: false
});
MyArray.push( {
 name: 'C',
 valueA: 55,
 valueB: 75,
 enabled: true
});
.
.
.

that's why I am looking for the max and min of ones that are with state true, excluding the ones that are false...

I tried to implement:

Array.minElement = function(array, prop) {
 return Math.min.apply(Math,
 array.filter(function(arr) { return arr['enabled']; })
 .map(function(arr) { return arr[prop]; })
 );
}
Array.maxElement = function(array, prop) {
 return Math.max.apply(Math,
 array.filter(function(arr) { return arr['enabled']; })
 .map(function(arr) { return arr[prop]; })
 );
}

so I should call like Array.minElement(MyArray, 'valueA') to obtain the minimum but looks like it doesn't work....and it should return the min...

what I did wrong here?...

Thanks at all Cheers Luigi

• Jose: Show us what you've tried
• georg: You probably mean [['A',40,true],['B',20,false].... In the current form, it's an array of four booleans.
• Andy: Can you show us what you've tried, and your expected output?

Answer 1

If MyArray looks like:

var MyArray = [['A', 40, true], ['B', 20, false], ['C', 55, true], ['D', 17, true]]

I’d do a combination of filter and map to get the array, then apply a Math method:

Math.max.apply(Math, 
 MyArray.filter(function(arr) { return arr[2]; })
 .map(function(arr) { return arr[1]; })
); // => 55

Answer 2

At the end I re-implemented minElement and maxElement like this:

Array.minElement = function(array, prop) {
 var lowest = Number.POSITIVE_INFINITY;
 for (var i=array.length-1; i>=0; i--) {
 if (parseFloat(array[i][prop]) < lowest) lowest = parseFloat(array[i][prop]);
 }
 return lowest;
}
Array.maxElement = function(array, prop) {
 var highest = Number.NEGATIVE_INFINITY;
 for (var i=array.length-1; i>=0; i--) {
 if (parseFloat(array[i][prop]) > highest) highest = parseFloat(array[i][prop]);
 } 
 return highest;
}

and now it works well

Answer 3

Arrays cannot really be extended but here's an example.

var createSpecialArray = (function () {
 function max() {
 return this.reduce(function (maxVal, item) {
 var val = item[1];
 return item[2]? 
 ((maxVal === null || maxVal < val)? val : maxVal) : 
 maxVal;
 }, null);
 }
 return function createSpecialArray() {
 var arr = Array.apply([], arguments);
 arr.max = max;
 return arr;
 };
})();

Then you can do something like:

var myArray = createSpecialArray(['A', 40, true], ['B', 20, false], ['C', 55, true], ['D', 17, true]);
console.log(myArray.max()); //55