PHP array_merge With Detailed Explanation

In this article, we will learn about the PHP array_merge function with a detailed explanation as well as sample programs that can be used and applied to your projects.

What is array_merge function in PHP?

In PHP, array_merge() is a built-in function which used to (merge) two or more arrays into a single array. 

In addition, the merging occurs in a way in which the values of the single array were appended at the end of the previous array.

This function also takes a list of arrays which is separated by commas as a parameter that needs to be merged and returns a new set of arrays with a merged value of arrays passed as a parameter.

Syntax:

array_merge(array1, array2, array3, ...)

Parameter values:

For example:

<?php

// php 7.4
$x = array("Glenn","Jude");
$y = array("Adones","Paul");
print_r(array_merge($x,$y));

?>

Output:

Array
(
    [0] => Glenn
    [1] => Jude
    [2] => Adones
    [3] => Paul
)

Merging two simple arrays in PHP

The array_merge() function can also pass two or more arrays, then the values of one array are appended at the end of the previous array. Once the two elements have the same key strings and then the latter value will override and match string keys.

Then integer keys will be rearranged which started to be from zero.

For example:

<?php

// array 0
$my_array1 = array("name" => "big", 2,26 );
$my_array2 = array("x", "y", "name" => "Glenn Magada Azuelo",
						"Position" => "Writer", 4);
$res = array_merge($my_array1, $my_array2);

print_r($res);

?>

Output:

Array
(
    [name] => Glenn Magada Azuelo
    [0] => 2
    [1] => 26
    [2] => x
    [3] => y
    [Position] => Writer
    [4] => 4
)

Passing parameter with integer keys in PHP

The array_merge() function can also be passed a parameter with integer keys. Once the keys of the parameter are integer, then the output array will be rearranged starting from 0 and will increment for the next elements by 1.

For example:

<?php

$my_array = array(1 => "IT SOURCE CODE", 3=>"FOR", 2=>"INFORMATION TECHNOLOGY STUDENTS");

$pies = array_merge($my_array);
print_r($pies);

?>

Output:

Array
(
    [0] => IT SOURCE CODE
    [1] => FOR
    [2] => INFORMATION TECHNOLOGY STUDENTS
)

PHP array_merge_recursive unique

The array_merge_recursive() is a function used to merge elements from one or more arrays together so that the (values) of the one can be appended at the end of the previous one and will return a resulting array.

In addition, once the input arrays are the same string keys, then the values of all the keys are merged together into an (array), and the entire process is done recursively so that if one of the values contains an array itself, the function will automatically merge with its corresponding entry into another array too.

However, if the arrays contain the same numeric key the key will be renumbered, Then original value will not overwrite the previous value, but will be appended successfully and returns a new array.

Syntax:

array_merge_recursive(array ...$arrays): array

For example:

<?php

$ar1 = array("name" => array("Glenn Magada Azuelo" => "red"), 5);
$ar2 = array(10, "name" => array("Glenn Magada Azuelo" => "green", "blue"));
$result = array_merge_recursive($ar1, $ar2);
print_r($result);

?>

Output:

Array
(
    [name] => Array
        (
            [Glenn Magada Azuelo] => Array
                (
                    [0] => red
                    [1] => green
                )

            [0] => blue
        )

    [0] => 5
    [1] => 10
)

Array merge multidimensional PHP

In PHP, merging a multidimensional array is very similar to a simple array. It will only take two arrays as input and merge them.

Furthermore, the multidimensional array index is automatically assigned in an increment order and automatically appended after the parent array elements.

Now let’s see three example programs below.

First example:

<?php
$arr = [
            [
                'name' => 'Glenn Magada Azuelo', 
                'address' => 'Philippines'
            ]
];
$arr2 = [
            [
                'name' => 'Angel Jude Suarez', 
                'address' => 'Philippines'
            ]
];
print_r(array_merge($arr, $arr2));

Output:

Array
(
    [0] => Array
        (
            [name] => Glenn Magada Azuelo
            [address] => Philippines
        )

    [1] => Array
        (
            [name] => Angel Jude Suarez
            [address] => Philippines
        )

)

Second example:

<?php
$permanent_location = [
    'employee name' => [
        'address' => 'Glenn Magada Azuelo'
    ]
];
$employment_location = [
    'employee name' => [
        'address' => 'PH'
    ]
];
print_r(array_merge($permanent_location, $employment_location));

Output:

Array
(
    [employee name] => Array
        (
            [address] => PH
        )

)

Third example:

<?php

$permanent_location = [
    'employeehome' => [
        'address' => 'PH'
    ]
];
$employment_location = [
    'employeecurrent' => [
        'address' => 'PH'
    ]
];
print_r(array_merge($permanent_location, $employment_location));

Output:

Array
(
    [employeehome] => Array
        (
            [address] => PH
        )

    [employeecurrent] => Array
        (
            [address] => PH
        )

)

How can I connect two array in PHP?

The array_merge() function is the best way to connect two arrays and can also be used to merge two or more arrays into one array with numeric keys. In addition, this function is also used to merge elements or values of two or more arrays together in one key starting array.

PHP array_merge vs spread

In PHP, the spread operator provides a better performance rather than array_merge() function. For the reason of the spread, union operator is a language structure while the array_merge is purely a function.

More About Array

• Not in Array PHP (With Advanced Program Examples)
• Sort An Array PHP (With Example Programs)
• PHP Echo Array with Example
• PHP File To Array With Program Examples
• PHP Remove Element From Array With Examples

Summary

This article discussed the array_merge and also tackles what is array_merge function, merging two simple arrays, passing parameters with integer keys, PHP array_merge_recursive unique, array merge multidimensional PHP, and how can I connect two arrays, and array_merge vs spread.

I hope this lesson has helped you learn a lot. Check out my previous and latest articles for more life-changing tutorials that could help you a lot.

Common use cases for PHP array_merge With Detailed Explanation

• Data collection loops. Build arrays from database results with foreach and $result[] = $row.
• Filter records. array_filter() to remove rows that fail a validation check.
• Transform data. array_map() to convert IDs to names, or apply a formatter to each value.
• Aggregate values. array_sum(), array_reduce(), or count() for totals and statistics.
• Sorted display. usort() with a custom comparator for domain-specific ordering.

Working code example

<?php
$orders = [
    ["id" => 1, "amount" => 250, "status" => "paid"],
    ["id" => 2, "amount" => 100, "status" => "pending"],
    ["id" => 3, "amount" => 400, "status" => "paid"],
];

// Get only paid orders
$paid = array_filter($orders, fn($o) => $o["status"] === "paid");

// Sum their amounts
$total = array_sum(array_column($paid, "amount"));
echo "Total paid: $total"; // 650
?>

Common pitfalls

• Modifying array during foreach. Never unset() or add elements during a foreach loop. Use array_filter() or build a new array.
• Numeric vs string keys. array_merge() renumbers integer keys but preserves string keys. Use + operator for key-preserving union.
• Sort in-place vs return. sort() returns bool and modifies the array; array_map() returns a new array. Read carefully.
• Empty array handling. array_reduce() on empty array returns the initial value; array_sum() returns 0.

Best practices

• Use array destructuring. [$id, $name] = explode(“,”, $csvLine) is cleaner than array indexing.
• Type declarations for functions. Declare array parameter types for type safety.
• Prefer typed arrays via generics. PHP 8+ supports @param array<int, User> PHPDoc for static analysis.
• Avoid over-nesting. Deeply nested arrays are hard to reason about. Extract to a class or DTO.

Glenn Azuelo

Programmer & Technical Writer at PIES IT Solution

Glenn Azuelo is a programmer and writer at PIES IT Solution, author of 40+ PHP tutorials, Java capstone projects, and Python game guides at itsourcecode.com. Specializes in PHP built-in functions (string manipulation, arrays, filesystem, magic methods), Java Windows Forms projects for BSIT capstone (chat application, POS, faculty management, memory game), and Python game programming with Pygame (chess, blackjack, dice).

Expertise: PHP · PHP Tutorials · PHP Built-in Functions · PHP String Functions · PHP Array Functions · PHP Magic Methods · Java · Java Swing · Windows Forms · Python · Pygame · Capstone Projects  · View all posts by Glenn Azuelo →