How to do array comparison and exclusion using PHP

PHP, as a popular programming language, has many useful functions for converting and processing data. In PHP, array is a very important and commonly used data type. Each array consists of one or more key-value pairs. Sometimes we need to compare between two arrays to find the differences between them and exclude duplicate or useless values. In this article, we will explain how to do array comparison and exclusion using PHP.

1. Array comparison

1. array_diff function

array_diff() function is used to compare the difference between two or more arrays. It will Returns values ​​that occur only in the first array and not in other arrays. It accepts two or more arrays as parameters. Here is a sample code that uses the array_diff() function to compare two arrays:

$array1 = array("a" => "red", "b" => "green", "c" => "blue");
$array2 = array("a" => "yellow", "b" => "green");
$result = array_diff($array1, $array2);
print_r($result);

After executing the above code, the output result is:

Array
(
    [a] => red
    [c] => blue
)

The resulting array contains the "red" and The "blue" key-value pairs, while the "yellow" key-value pairs in $array2 are excluded.

2. array_intersect function

array_intersect() function is used to compare the intersection between two or more arrays. It will return the values ​​that appear in all arrays at the same time. It accepts two or more arrays as parameters. The following is a sample code that uses the array_intersect() function to compare two arrays:

$array1 = array("a" => "red", "b" => "green", "c" => "blue");
$array2 = array("a" => "yellow", "b" => "green");
$result = array_intersect($array1, $array2);
print_r($result);

After executing the above code, the output result is:

Array
(
    [b] => green
)

The resulting array only contains the elements in $array1 and $array2 "Green" key-value pairs because this is the intersection of two arrays.

2. Array Exclusion

In PHP, there are many functions that can exclude key-value pairs from arrays. The following are some commonly used functions:

1. unset function

PHP’s unset() function is used to remove specified elements from an array. The code example is as follows:

$array = array(1, 2, 3, 4, 5);
unset($array[3]);  // 删除数组下标为3的元素
print_r($array);

After executing the above code, the output result is:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [4] => 5
)

"4" is retained in the array, while "3" has been deleted.

2. array_splice function

PHP’s array_splice() function is used to remove specified elements from an array and insert new elements. It accepts four parameters: the array to be processed, the number of elements to delete, the starting position, and the number of elements to insert. The code example is as follows:

$array = array(1, 2, 3, 4, 5);
array_splice($array, 2, 1);  // 删除从下标为2的元素开始的一个元素
print_r($array);

After executing the above code, the output result is:

Array
(
    [0] => 1
    [1] => 2
    [2] => 4
    [3] => 5
)

"3" is retained in the array, while "4" has been deleted.

3. array_filter function

array_filter() function is used to filter out qualified elements from an array. It accepts two parameters, the first parameter is to be processed Array, the second parameter is a callback function, which is used to define the filter conditions. The code example is as follows:

function is_even($n) {
    return ($n % 2 == 0);   // 如果数字是偶数返回true
}
$array = array(1, 2, 3, 4, 5);
$result = array_filter($array, "is_even");   // 仅保留偶数
print_r($result);

After executing the above code, the output result is:

Array
(
    [1] => 2
    [3] => 4
)

"1", "3", and "5" are all excluded from the result array because they are not even.

Summary

The above is about the methods of comparing arrays and excluding elements in PHP. Using these methods can more conveniently operate and convert arrays, thereby better processing and managing data. In actual development, we can choose appropriate methods to solve problems according to specific needs.

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