Can't concatenate 2 arrays in PHP

Question

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?

Answer 1

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.

Answer 2

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

Answer 3

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.

Answer 4

Specifying a key for each array member works

$array = array(0 => 'Item 1');

$array += array(1 => 'Item 2');

var_dump($array);

produces

array(2) { [0]=> string(6) "Item 1" [1]=> string(6) "Item 2" }

Answer 5

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.

Answer 6

$array = array('Item 1');

array_push($array,'Item 2');

or

$array[] = 'Item 2';

Answer 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.

Answer 8

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'));