How to write array intersection in php

PHP is a scripting language widely used in web development. It is popular for its flexibility, efficiency and ease of learning. In PHP, array is a common data structure that allows us to store and process large amounts of data. This article will introduce you how to use PHP to write array intersection.

Array intersection refers to the set of elements that co-exist in two or more arrays. In PHP, we can use array_intersect() function to find the intersection between two arrays. This function accepts any number of arguments and returns the intersection between all arrays.

The following is a sample code:

<?php
$array1 = array(1, 2, 3, 4, 5);
$array2 = array(3, 4, 5, 6, 7);

$result = array_intersect($array1, $array2);

print_r($result); // 输出： Array ( [2] => 3 [3] => 4 [4] => 5 )
?>

In the above code, we first define two arrays $array1 and $array2, which contain some values. We then use the array_intersect() function to find the intersection between these two arrays and save the result in the $result variable. Finally, we use the print_r() function to print the results.

Running the above code will output the following results:

Array ( [2] => 3 [3] => 4 [4] => 5 )

This is an array containing three elements, each element is a value that exists in the two arrays. Among them, the key name represents the index position of the element in the $array1 array, and the value represents the value of the element.

If we want to find the intersection between multiple arrays, just add more parameters to the array_intersect() function. For example:

<?php
$array1 = array(1, 2, 3, 4, 5);
$array2 = array(3, 4, 5, 6, 7);
$array3 = array(5, 6, 7, 8, 9);

$result = array_intersect($array1, $array2, $array3);

print_r($result); // 输出： Array ( [4] => 5 )
?>

In the above code, we added another array $array3 and passed it as the third parameter of the array_intersect() function. In the end, we only got one intersection element, the element with value 5.

It should be noted that the array_intersect() function ignores key names and only compares based on values. If you need to retain the key names of the original array, you can use the array_intersect_assoc() function for comparison. This function is very similar to the array_intersect() function, except that it compares keys and values ​​at the same time.

<?php
$array1 = array(&#39;a&#39; => 1, 'b' => 2, 'c' => 3);
$array2 = array('c' => 3, 'd' => 4, 'e' => 5);
$array3 = array('e' => 5, 'f' => 6, 'g' => 7);

$result = array_intersect_assoc($array1, $array2, $array3);

print_r($result); // 输出： Array ( [e] => 5 )
?>

In the above code, we define three arrays with key names, and then use the array_intersect_assoc() function to compare. The result is an array with a key named 'e' and a value of 5, which is the only intersection element among the three arrays.

In this article, we introduced how to write array intersection using PHP. We can use the array_intersect() function to find the intersection between any number of arrays, or we can use the array_intersect_assoc() function to retain the key names of the original array. These functions can help us quickly process and analyze large amounts of data in web development.

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