CODEWITHSUNDEEP
phparraysconcatenation
alex
alex

Reputation: 490413

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?

Upvotes: 84

Views: 142562

Answers (11)

awgy
awgy

Reputation: 16924

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;

Upvotes: 166

Nir Alfasi
Nir Alfasi

Reputation: 53535

I believe answers suggesting array_merge() are incorrect. 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);
?>

Upvotes: 8

Sergio A. Kessler
Sergio A. Kessler

Reputation: 436

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/

Upvotes: 15

Henry
Henry

Reputation: 7891

This works for non-associative arrays:

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

Upvotes: 0

randomWalk
randomWalk

Reputation: 1

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

Upvotes: -6

Rupert Madden-Abbott
Rupert Madden-Abbott

Reputation: 13298

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'));

Upvotes: 3

deceze
deceze

Reputation: 522372

+ 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.

Upvotes: 7

Brant Messenger
Brant Messenger

Reputation: 1451

$array = array('Item 1');

array_push($array,'Item 2');

or

$array[] = 'Item 2';

Upvotes: 2

Rabbott
Rabbott

Reputation: 4332

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.

Upvotes: 3

Christopher Altman
Christopher Altman

Reputation: 4896

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.

Upvotes: 12

Josh K
Josh K

Reputation: 28893

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.

Upvotes: -3

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