JavaScript Sorting Arrays
Alpabetic SortArray sort()Array reverse() Array toSorted() Array toReversed() Sorting Objects See Also:Basic MethodsSearch Methods Iteration Methods |
Numeric SortNumeric SortRandom Sort Math.min() Math.max() Home made Min() Home made Max() |
Sorting an Array
The sort() method sorts an array alphabetically:
Reversing an Array
The reverse() method reverses the elements in an array:
By combining sort() and reverse(),
you can sort an array in descending order:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();
fruits.reverse();
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JavaScript Array toSorted() Method
ES2023 added the toSorted() method as a safe way
to sort an array without altering the original array.
The difference between toSorted() and sort()
is that the first method creates a new array, keeping the original array unchanged, while the last method alters the original array.
Example
const months = ["Jan", "Feb", "Mar", "Apr"];
const sorted = months.toSorted();
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JavaScript Array toReversed() Method
ES2023 added the toReversed() method as a safe way
to reverse an array without altering the original array.
The difference between toReversed() and reverse() is that the first method
creates a new array, keeping the original array unchanged, while the last method alters the original array.
Example
const months = ["Jan", "Feb", "Mar", "Apr"];
const reversed = months.toReversed();
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Numeric Sort
By default, the sort() function sorts values as strings.
This works well for strings ("Apple" comes before "Banana").
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
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
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Use the same trick to sort an array descending:
Example
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b - a});
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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){return 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.
If the result is negative, a is sorted before
b.
If the result is positive, b is sorted
before a.
If the result is 0, no changes are done with the sort order of the two values.
Example:
The compare function compares all the values in the array, two values at a
time (a, b).
When comparing 40 and 100, the sort() method calls the compare function(40, 100).
The function calculates 40 - 100 (a - b), and
since the result is negative (-60), 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>
const 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){return
a - b});
document.getElementById("demo").innerHTML = points;
}
</script>
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Sorting an Array in Random Order
Using a sort function, like explained above, you can sort an numeric array in random order
Example
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(){return 0.5 - Math.random()});
The Fisher Yates Method
The points.sort() method in the example above is not accurate. It will favor some numbers over others.
The most popular correct method, is called the Fisher Yates shuffle, and was introduced in data science as early as 1938!
In JavaScript the method can be translated to this:
Example
const points = [40, 100, 1, 5, 25, 10];
for (let i = points.length -1; i > 0; i--) {
let j = Math.floor(Math.random() * (i+1));
let k = points[i];
points[i] = points[j];
points[j] = k;
}
Find the Lowest (or Highest) Array Value
There are no built-in functions for finding the max or min value in an array.
To find the lowest or highest value you have 3 options:
- Sort the array and read the first or last element
- Use Math.min() or Math.max()
- Write a home made function
Find Min or Max with sort()
After you have sorted an array, you can use the index to obtain the highest and lowest values.
Sort Ascending:
Example
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
// now points[0] contains the lowest value
// and points[points.length-1] contains the highest value
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Sort Descending:
Example
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b - a});
// now points[0] contains the highest value
// and points[points.length-1] contains the lowest value
Try it Yourself »
Note
Sorting a whole array is a very inefficient method if you only want to find the highest (or lowest) value.
Using Math.min() on an Array
You can use Math.min.apply to find the lowest number in an array:
Math.min.apply(null, [1, 2, 3]) is equivalent to Math.min(1, 2, 3).
Using Math.max() on an Array
You can use Math.max.apply to find the highest number in an array:
Math.max.apply(null, [1, 2, 3]) is equivalent to Math.max(1, 2, 3).
JavaScript Array Minimum Method
There is no built-in function for finding the lowest value in a JavaScript array.
The fastest code to find the lowest number is to use a home made method.
This function loops through an array comparing each value with the lowest value found:
Example (Find Min)
function myArrayMin(arr) {
let len = arr.length;
let min = Infinity;
while (len--) {
if (arr[len] < min) {
min = arr[len];
}
}
return min;
}
JavaScript Array Maximum Method
There is no built-in function for finding the highest value in a JavaScript array.
The fastest code to find the highest number 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) {
let len = arr.length;
let max = -Infinity;
while (len--) {
if (arr[len] > max) {
max = arr[len];
}
}
return max;
}
Sorting Object Arrays
JavaScript arrays often contain objects:
Example
const cars = [
{type:"Volvo", year:2016},
{type:"Saab", year:2001},
{type:"BMW", year:2010}
];
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:
Comparing string properties is a little more complex:
Example
cars.sort(function(a, b){
let x = a.type.toLowerCase();
let y = b.type.toLowerCase();
if (x < y) {return -1;}
if (x > y) {return 1;}
return 0;
});
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Stable Array sort()
ES2019 revised the Array sort() method.
Before 2019, the specification allowed unstable sorting algorithms such as QuickSort.
After ES2019, browsers must use a stable sorting algorithm:
When sorting elements on a value, the elements must keep their relative position to other elements with the same value.
Example
const myArr = [
{name:"X00",price:100 },
{name:"X01",price:100 },
{name:"X02",price:100 },
{name:"X03",price:100 },
{name:"X04",price:110 },
{name:"X05",price:110 },
{name:"X06",price:110 },
{name:"X07",price:110 }
];
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In the example above, when sorting on price, the result is not allowed to come out with the names in an other relative position like this:
X01 100
X03 100
X00 100
X03 100
X05 110
X04 110
X06 110
X07 110
Complete Array Reference
For a complete Array reference, go to our:
Complete JavaScript Array Reference.
The reference contains descriptions and examples of all Array properties and methods.
