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JavaScript Sorting Arrays


The sort() method is one of the strongest array methods.


Sorting an Array

The sort() method sorts an array alphabetically:

Example

var fruits = [“Banana”, “Orange”, “Apple”, “Mango”];
fruits.sort();            // Sorts the elements of fruits

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Reversing an Array

The reverse() method reverses the elements in an array.

You can use it to sort an array in descending order:

Example

var fruits = [“Banana”, “Orange”, “Apple”, “Mango”];
fruits.sort();            // Sorts the elements of fruits
fruits.reverse();         // Reverses the order of the elements

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Numeric Sort

By default, the sort() function sorts values as strings.

This works well for strings (“Apple” comes before “Banana”).

However, if numbers are sorted as strings, “25” is bigger than “100”, because “2” is bigger than “1”.

Because of this, the sort() method will produce incorrect result when sorting numbers.

You can fix this by providing a compare function:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b));

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Use the same trick to sort an array descending:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b));

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The Compare Function

The purpose of the compare function is to define an alternative sort order.

The compare function should return a negative, zero, or positive value, depending on the arguments:

function(a, b)

When the sort() function compares two values, it sends the values to the compare function, and sorts the values according to the returned (negative, zero, positive) value.

Example:

When comparing 40 and 100, the sort() method calls the compare function(40,100).

The function calculates 40-100, and returns -60 (a negative value).

The sort function will sort 40 as a value lower than 100.

You can use this code snippet to experiment with numerically and alphabetically sorting:

<button onclick=”myFunction1()”>Sort Alphabetically</button>
<button onclick=”myFunction2()”>Sort Numerically</button>

<p id=”demo”></p>

<script>
var points = [40, 100, 1, 5, 25, 10];
document.getElementById(“demo”).innerHTML = points;

function myFunction1() {
points.sort();
document.getElementById(“demo”).innerHTML = points;
}
function myFunction2() {
points.sort(function(a, b));
document.getElementById(“demo”).innerHTML = points;
}
</script>

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Sorting an Array in Random Order

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b));

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Find the Highest (or Lowest) Array Value

There are no built-in functions for finding the max or min value in an array.

However, after you have sorted an array, you can use the index to obtain the highest and lowest values.

Sorting ascending:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b));
// now points[0] contains the lowest value
// and points[points.length-1] contains the highest value

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Sorting descending:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b));
// now points[0] contains the highest value
// and points[points.length-1] contains the lowest value

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Sorting a whole array is a very inefficient method if you only want to find the highest (or lowest) value.


Using Math.max() on an Array

You can use Math.max.apply to find the highest number in an array:

Example

function myArrayMax(arr) {
return Math.max.apply(null, arr);
}

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Math.max.apply([1, 2, 3]) is equivalent to Math.max(1, 2, 3).


Using Math.min() on an Array

You can use Math.min.apply to find the lowest number in an array:

Example

function myArrayMin(arr) {
return Math.min.apply(null, arr);
}

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Math.min.apply([1, 2, 3]) is equivalent to Math.min(1, 2, 3).


My Min / Max JavaScript Methods

The fastest solution is to use a “home made” method.

This function loops through an array comparing each value with the highest value found:

Example (Find Max)

function myArrayMax(arr) {
var len = arr.length
var max = -Infinity;
while (len–) {
if (arr[len] > max) {
max = arr[len];
}
}
return max;
}

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This function loops through an array comparing each value with the lowest value found:

Example (Find Min)

function myArrayMin(arr) {
var len = arr.length
var min = Infinity;
while (len–) {
if (arr[len] < min) {
min = arr[len];
}
}
return min;
}

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Sorting Object Arrays

JavaScript arrays often contain objects:

Example

var cars = [
,
,
];

Even if objects have properties of different data types, the sort() method can be used to sort the array.

The solution is to write a compare function to compare the property values:

Example

cars.sort(function(a, b));

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Comparing string properties is a little more complex:

Example

 cars.sort(function(a, b){
var x = a.type.toLowerCase();
var y = b.type.toLowerCase();
if (x < y)
if (x > y)
return 0;
});

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Test Yourself with Exercises!

Exercise 1 »