How to use callback function to compare key names to calculate the intersection of arrays in PHP

php editor Youzi will introduce you in detail how to use the callback function to compare key names to calculate the intersection of arrays. In PHP, we can use the array_uintersect_assoc() function combined with a custom callback function to compare arrays based on key names and return the intersection result. Through concise code examples and step-by-step explanations, you will easily master this practical skill, making your PHP development more efficient and flexible.

PHP uses callback function to compare key names to calculate array intersection

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In order to calculate the intersection of two arrays, that is, elements that share the same key name, you can use the array_intersect_key() function of php. This function iterates through the first array and checks if an element with the same key exists in the second array using the provided callback function.

The following is the syntax of this function:

array_intersect_key(array $array1, array $array2, callable $key_compare_func)

in:

• $array1：The first array
• $array2: The second array
• $key_compare_func: Callback function for comparing key names

The callback function must accept two parameters, representing the two key names to be compared, and return a Boolean value indicating whether the two key names are equal.

The following example shows how to use the array_intersect_key() function to calculate the intersection of two arrays, โดยใช้ callback function เปรียบเทียบชื่อคีย์:

<?php

$array1 = ["apple" => "green", "banana" => "yellow", "orange" => "orange"];
$array2 = ["apple" => "red", "banana" => "green", "pear" => "green"];

//Define the callback function for comparing key names
$key_compare_func = function($key1, $key2) {
return $key1 === $key2;
};

// Calculate array intersection
$intersection = array_intersect_key($array1, $array2, $key_compare_func);

print_r($intersection);

?>

Output:

Array
(
[apple] => green
[banana] => green
)

In this example, the callback function $key_compare_func compares two key names for equality. Only the keys apple and banana exist in both arrays, so they form the intersection.

Use anonymous functions:

You can also use anonymous functions to define callback functions to make them more concise. Here is the same example using anonymous functions:

$intersection = array_intersect_key($array1, $array2, function($key1, $key2) {
return $key1 === $key2;
});

Using arrow functions (PHP 7.4 and above):

In PHP 7.4 and above, you can use arrow functions to further simplify your code:

$intersection = array_intersect_key($array1, $array2, fn($key1, $key2) => $key1 === $key2);

Custom key name comparison:

The callback function allows custom key name comparison logic. For example, you can use the following callback function to compare key names case-insensitively:

$key_compare_func = function($key1, $key2) {
return strtolower($key1) === strtolower($key2);
};

In this way, even if the key names of the arrays are in different cases, the intersection will be calculated correctly.

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