Can't concatenate 2 arrays in PHP

I've recently learned how to join 2 arrays using the + operator in PHP.

But consider this code...

$array = array('Item 1');

$array += array('Item 2');

var_dump($array);

Output is

> array(1) { [0]=> string(6) "Item > 1" }

Why does this not work? Skipping the shorthand and using $array = $array + array('Item 2') does not work either. Does it have something to do with the keys?

Both will have a key of 0, and that method of combining the arrays will collapse duplicates. Try using array_merge() instead.

$arr1 = array('foo'); // Same as array(0 => 'foo')
$arr2 = array('bar'); // Same as array(0 => 'bar')

// Will contain array('foo', 'bar');
$combined = array_merge($arr1, $arr2);

If the elements in your array used different keys, the + operator would be more appropriate.

$arr1 = array('one' => 'foo');
$arr2 = array('two' => 'bar');

// Will contain array('one' => 'foo', 'two' => 'bar');
$combined = $arr1 + $arr2;

Edit: Added a code snippet to clarify

Use array_merge()
See the documentation here:
http://php.net/manual/en/function.array-merge.php

> Merges the elements of one or more arrays together so that the values of one are appended to the end of the previous one. It returns the resulting array.

IMO some of the previous answers are incorrect! (It's possible to sort the answers to start from oldest to newest).

array_merge() actually merges the arrays, meaning, if the arrays have a common item one of the copies will be omitted. Same goes for + (union).

I didn't find a "work-around" for this issue, but to do it manually...

Here it goes:

<?php
$part1 = array(1,2,3);
echo "array 1 = \n";
print_r($part1);
$part2 = array(4,5,6);
echo "array 2 = \n";
print_r($part2);
$ans = NULL;
for ($i = 0; $i < count($part1); $i++) {
	$ans[] = $part1[$i];
}
for ($i = 0; $i < count($part2); $i++) {
	$ans[] = $part2[$i];
}
echo "after arrays concatenation:\n";
print_r($ans);
?>

use the splat ( or spread ) operator:

  $animals = ['dog', 'cat', 'snake', 'pig', 'chicken'];
  $fruits = ['apple', 'banana', 'water melon'];
  $things = [...$animals, ...$fruits];

source: https://www.kindacode.com/article/merging-arrays-in-php-7/

+ is called the Union operator, which differs from a Concatenation operator (PHP doesn't have one for arrays). The description clearly says:

> The + operator appends elements of remaining keys from the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

With the example:

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");
$c = $a + $b;

array(3) {
  ["a"]=>
  string(5) "apple"
  ["b"]=>
  string(6) "banana"
  ["c"]=>
  string(6) "cherry"
}

Since both your arrays have one entry with the key 0, the result is expected.

To concatenate, use array_merge.

Try array_merge.

$array1 = array('Item 1');

$array2 = array('Item 2');

$array3 = array_merge($array1, $array2);

I think its because you are not assigning a key to either, so they both have key of 0, and the + does not re-index, so its trying to over write it.

It is indeed a key conflict. When concatenating arrays, duplicate keys are not overwritten.

Instead you must use array_merge()

$array = array_merge(array('Item 1'), array('Item 2'));

$array = array('Item 1');

array_push($array,'Item 2');

or

$array[] = 'Item 2';

This works for non-associative arrays:

while(($item = array_shift($array2)) !== null && array_push($array1, $item));

Try saying

$array[] = array('Item 2'); 

Although it looks like you're trying to add an array into an array, thus $array[][] but that's not what your title suggests.

you may use operator . $array3 = $array1.$array2;