How to Check If Two Arrays are Equal in PHP?

PHP array equality check method

In PHP, determining whether the two arrays are equal means that the array elements are the same, the order is consistent, and even the data types match. This article will introduce several methods to check array equality in PHP:

1. Violence Law

   This method first sorts the two arrays and then compares them using the == operator. Sort to ensure that the order of elements does not affect the comparison results.

   Example:

   <?php
   $array1 = [3, 2, 1];
   $array2 = [1, 2, 3];
   
   sort($array1);
   sort($array2);
   
   if ($array1 == $array2) {
       echo "数组相等";
   } else {
       echo "数组不相等";
   }
   ?>

   Output:

   <code>数组相等</code>

   Time complexity: O(n log n) Space Complexity: O(1)

2. Use the == operator

   This is a way to directly compare array elements. The == operator checks whether the two arrays are the same size and contain the same elements, and the order must also be the same. This method is simple and easy to use, but it is not strict with data types. For example, integer 3 and string '3' are considered equal.

   Example:

   <?php
   $arr1 = [1, 2, 3, 4];
   $arr2 = [1, 2, 3, 4];
   
   if ($arr1 == $arr2) {
       echo "数组相等";
   } else {
       echo "数组不相等";
   }
   ?>

   Output:

   <code>数组相等</code>

   Time complexity: O(n) Space Complexity: O(1)

3. Use array_diff()Methods

   This is a built-in function for PHP to find the differences between two arrays. If array_diff() returns an empty array, it means that the two arrays are equal. This method is often used to compare arrays of disordered and unique elements.

   Example:

   <?php
   $array1 = [1, 2, 3];
   $array2 = [3, 2, 1];
   
   if (empty(array_diff($array1, $array2)) && empty(array_diff($array2, $array1))) {
       echo "数组相等";
   } else {
       echo "数组不相等";
   }
   ?>

   Output:

   <code>数组相等</code>

   Time complexity: O(n) Space Complexity: O(n)

4. Use the === operator

   === operator performs strict array element comparison, it checks:

   • Is the size of the two arrays the same?
   • Whether two arrays contain the same elements must also be the same in the order
   • Is the data type of the element the same?

   Return false if any condition is not satisfied. This method makes a more accurate comparison by considering the types.

   Example:

   <?php
   $array1 = [1, 2, 3, 4];
   $array2 = [1, 2, '3', 4];
   
   if ($array1 === $array2) {
       echo "数组相等";
   } else {
       echo "数组不相等";
   }
   ?>

   Output:

   <code>数组不相等</code>

   Time complexity: O(n) Space Complexity: O(1)

Which method to choose depends on the specific application scenario and the requirements for data type matching. If strict type check is required, use the === operator; if it is not sensitive to type, use the == operator or array_diff() method. For unordered arrays, the array_diff() method is more suitable. Although brute force methods can handle disordered arrays, they are relatively inefficient.

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