Merging with array_merge()

PHP course · Beginner · Lesson 61/116

Learn to merge two arrays into one with array_merge().

Merging with array_merge()

array_merge() combines two or more arrays into one. Think of placing two arrays end to end. array_merge($a, $b) lists the elements of $a first, then the elements of $b.

For arrays with numeric indexes, the elements are re-indexed: 0, 1, 2, ... in order. The merged array has a total length equal to the sum of the two arrays.

Numeric and string keys

array_merge() behaves differently with numeric and string indexes. Numeric indexes are always renumbered; so [5 => "a"] and [7 => "b"] merge into [0 => "a", 1 => "b"].

String keys are overwritten: if the same key exists, the value from the last array wins. For example, array_merge(["name" => "Alex"], ["name" => "Sam"]) yields ["name" => "Sam"]; the first "Alex" is lost. Watch out for matching keys.

Exercise Merge two lists

Define two arrays: $letters = ["A", "B"] and $more = ["C", "D"]. Use array_merge() to combine them into $all. Then walk through them with foreach ($all as $letter) and print each element on its own line with echo $letter . "\n".

Show example solution

First merge with $all = array_merge($letters, $more);. Then loop with foreach ($all as $letter) { echo $letter . "\n"; } and print.
Example solution:
<?php
$letters = ["A", "B"];
$more = ["C", "D"];
// Merge two lists and print them
$all = array_merge($letters, $more);
foreach ($all as $letter) {
    echo $letter . "\n";
}

Test yourself

What does array_merge do?
- Sorts an array
- Merges two arrays
- Removes an element
- Reverses an array
Show answer

Merges two arrays — Correct. array_merge combines two or more arrays into one.

Complete merging two arrays

$a = [1, 2];
$b = [3, 4];
$merged = ____($a, $b);
print_r($merged);

Show answer

$a = [1, 2];
$b = [3, 4];
$merged = array_merge($a, $b);
print_r($merged);

Match each case to its result

Numeric indexes

Renumbered
String keys

Last value wins
Merging empty array

Other array returns
What is the output of the code below?
```
$a = [1, 2];
$b = [3, 4];
print_r(array_merge($a, $b));
```
- [1, 2, 3, 4]
- [1, 2]
- [3, 4]
- [3, 4, 1, 2]
Show answer

[1, 2, 3, 4] — Correct. array_merge lists $a's elements first, then $b's.

Merging with array_merge()