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C # tutorial
The sort() method sorts an array alphabetically
The sort()
method sorts an array alphabetically:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();
The reverse()
method reverses the elements in an array.
You can use it to sort an array in descending order:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();
fruits.reverse();
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:
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
Use the same trick to sort an array descending:
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b - a});
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.
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>
const points = [40, 100, 1, 5, 25, 10];
points.sort(function(){return 0.5 - Math.random()});
The above example, array.sort(), is not accurate, it will favor some numbers over the 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:
const points = [40, 100, 1, 5, 25, 10];
for (let i = points.length -1; i > 0;
i--) {
let j = Math.floor(Math.random() * i)
let k = points[i]
points[i] = points[j]
points[j] = k
}
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:
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
Sorting descending:
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
Sorting a whole array is a very inefficient method if you only want to find the highest (or lowest) value.
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)
.
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)
.
The fastest solution is to use a "home made" method.
This function loops through an array comparing each value with the highest value found:
function myArrayMax(arr) {
let len = arr.length;
let max = -Infinity;
while (len--) {
if (arr[len] > max) {
max = arr[len];
}
}
return max;
}
This function loops through an array comparing each value with the lowest value found:
function myArrayMin(arr) {
let len = arr.length;
let min = Infinity;
while (len--) {
if (arr[len] < min) {
min = arr[len];
}
}
return min;
}
JavaScript arrays often contain objects:
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:
cars.sort(function(a, b){return a.year - b.year});
Comparing string properties is a little more complex:
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;
});
For a complete Array reference, go to our:
Complete JavaScript Array Reference.
The reference contains descriptions and examples of all Array properties and methods.
Use the correct Array method to sort the fruits
array alphabetically.
const fruits = ["Banana", "Orange", "Apple", "Kiwi"]; ;