usort sorting by user defined comparison function

We can sort an array by using some non-trivial criteria in PHP by using a user defined comparison function. In the function usort we can use our own sort criteria by using one function.

You can read many standard way of sorting the array given here.

Example : Sorting in the order of length

Here is the user defined function has to have some matching requirements. One is it has to accept two variables. It should return either 0,less than 0 or greater than 0 based on the matching where first element is less than , equal to or greater than second element.

After the sorting the small word ( by length ) will be at the first and the longest word will to the end.

This usort function does not retain the associated index or the key of the elements of the array.

<?Php
function compare($x,$y){
$x=strlen($x);
$y=strlen($y);
if($x==$y){
return 0;
}
 return ($x < $y) ? -1 : 1;
}

$input = array ("Pineapple", "Orange", "Banana", "Mango", "Apple","Strawberry","aaa","bb");
while (list ($key, $val) = each ($input)) {
echo "$key -> $val <br>";
}
usort($input, "compare");
echo "<br>-----After usort---------<br>";
while (list ($key, $val) = each ($input)) {
echo "$key -> $val <br>";
}
?>

Here is the output of usort function where user defined comparisons function is used


0 -> Pineapple 
1 -> Orange 
2 -> Banana 
3 -> Mango 
4 -> Apple 
5 -> Strawberry 
6 -> aaa 
7 -> bb 

-----After usort---------
0 -> bb 
1 -> aaa 
2 -> Apple 
3 -> Mango 
4 -> Orange 
5 -> Banana 
6 -> Pineapple 
7 -> Strawberry

Example: Sorting a Multidimensional Array by a Key

$array = [
    ['name' => 'John', 'age' => 25],
    ['name' => 'Anna', 'age' => 22],
    ['name' => 'Mike', 'age' => 30]
];
usort($array, function($a, $b) {
    return $a['age'] - $b['age'];
});
print_r($array);

output

Array ( [0] => Array ( [name] => Anna [age] => 22 ) [1] => Array ( [name] => John [age] => 25 ) [2] => Array ( [name] => Mike [age] => 30 ) )

Example: Case-Insensitive String Sorting

$array = ['Banana', 'apple', 'Cherry'];
usort($array, 'strcasecmp');
print_r($array);

Array ( [0] => apple [1] => Banana [2] => Cherry )

Check how file modification time of all files inside a directory is sorted by using usort()
Array REFERENCE array_multisort() :Sorting Multiple Arrays

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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usort: sorting by user defined function

Example : Sorting in the order of length

Example: Sorting a Multidimensional Array by a Key

Example: Case-Insensitive String Sorting

Subhendu Mohapatra