Specify the basis for removing duplicate elements when deduplicating PHP arrays

PHP’s array_unique() function is used to remove duplicate elements from an array, and its default use is strict equality (===). We can specify the basis for deduplication through a custom comparison function: create a custom comparison function and specify the deduplication standard (for example, based on element length); pass the custom comparison function as the third parameter to the array_unique() function. Remove duplicate elements based on specified criteria.

Use the PHP array_unique() function to specify the basis for deduplication

Introduction

_unique() Function is used to remove duplicate elements from an array. By default, it uses strict equality (===) to determine duplicate elements. However, we can remove duplicate elements based on different criteria by providing a custom comparison function to specify the basis for deduplication.

Code example

<?php

// 创建一个包含重复元素的数组
$arr = array(
    'a', 'b', 'c', 'd',
    'a', 'c', 'e', 'f'
);

// 使用默认的严格相等比较器去除重复元素
print_r(array_unique($arr));

// 自定比较器，根据元素长度去除重复元素
$length_comparator = function($a, $b) {
    return strlen($a) == strlen($b);
};

// 使用自定比较器去除重复元素
print_r(array_unique($arr, SORT_REGULAR, $length_comparator));

?>

Output result

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
    [5] => f
)
Array
(
    [0] => a
    [1] => b
    [2] => c
    [4] => d
    [6] => e
)

Actual case

Suppose we have an array of student objects, each object has a name and age. We can use the _unique() function and a custom comparator to remove students with the same age:

<?php

class Student {
    public $name;
    public $age;
}

// 创建一个包含具有相同年龄的学生对象的数组
$students = array(
    new Student('Alice', 20),
    new Student('Bob', 20),
    new Student('Carol', 21),
    new Student('Dave', 21),
);

// 自定比较器，根据学生的年龄去除重复元素
$age_comparator = function($a, $b) {
    return $a->age == $b->age;
};

// 使用自定比较器去除重复元素
$unique_students = array_unique($students, SORT_REGULAR, $age_comparator);

// 打印唯一学生的姓名
foreach ($unique_students as $student) {
    echo $student->name . '<br>';
}

?>

Output result

Alice
Carol

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