PHP Array Merge: An In-Depth Guide

The PHP array_merge() function is a powerful tool for combining arrays into a single array. This function takes two or more arrays as arguments and merges them into a single array, with the values of the later arrays overwriting the values of the previous arrays. In this guide, we will dive deep into the array_merge() function, exploring its various uses and applications.

Basic Usage of array_merge()

The basic usage of the array_merge() function is straightforward. Simply pass in two or more arrays as arguments, and the function will return a new array that is the result of merging the arrays. Here is an example:

<?php

$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "rectangle", 4);
$result = array_merge($array1, $array2);
print_r($result);

?>

Output:

Array
(
    [color] => green
    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => rectangle
    [4] => 4
)

As you can see, the values from $array2 overwrite the values of $array1 when they have the same key.

Merging Multidimensional Arrays

The array_merge() function can also be used to merge multidimensional arrays. To merge multidimensional arrays, simply pass in each array as an argument to the function. Here is an example:

<?php

$array1 = array("color" => array("favorite" => "red"), 2, 4);
$array2 = array("a", "b", "color" => array("favorite" => "green"), "shape" => "rectangle", 4);
$result = array_merge_recursive($array1, $array2);
print_r($result);

?>

Output:

Array
(
    [color] => Array
        (
            [favorite] => green
        )
    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => rectangle
    [4] => 4
)

Note that in this example, we used the array_merge_recursive() function instead of array_merge(). This is because array_merge_recursive() is used to merge multidimensional arrays, whereas array_merge() is used to merge flat arrays.

Merging an Indexed Array with an Associative Array

When merging an indexed array with an associative array, the values from the associative array will overwrite the values of the indexed array when they have the same key. Here is an example:

<?php

$array1 = array("a", "b", "c");
$array2 = array("a" => "apple", "b" => "banana", "c" => "cherry");
$result = array_merge($array1, $array2);
print_r($result);

?>

Output:

Array
(
    [0] => a
    [1] => b
    [2] => c
    [a] => apple
    [b] => banana
    [c] => cherry
)

As you can see, the values from $array2 overwrite the values of $array1 when they have the same key. This is an important thing to keep in mind when merging arrays with different types.

Merging an Associative Array with an Indexed Array

The result of merging an associative array with an indexed array is similar to the result of merging an indexed array with an associative array. The values from the associative array will overwrite the values of the indexed array when they have the same key. Here is an example:

<?php

$array1 = array("a" => "apple", "b" => "banana", "c" => "cherry");
$array2 = array("a", "b", "c");
$result = array_merge($array1, $array2);
print_r($result);

?>

Output:

Array
(
    [a] => apple
    [b] => banana
    [c] => cherry
    [0] => a
    [1] => b
    [2] => c
)

As you can see, the values from $array2 overwrite the values of $array1 when they have the same key.

Performance Considerations

The array_merge() function has a linear time complexity, meaning that the time it takes to merge arrays increases linearly with the size of the arrays. For this reason, it's important to keep the number of arrays being merged to a minimum, and to avoid using the function on extremely large arrays.

Conclusion

The array_merge() function is a versatile tool for combining arrays in PHP. Whether you're merging flat arrays, multidimensional arrays, indexed arrays, or associative arrays, this function has you covered. With its linear time complexity, it's important to keep the size of the arrays being merged to a minimum, but with the right approach, this function can be an invaluable tool in your PHP toolkit.