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array_merge

(PHP 4, PHP 5, PHP 7, PHP 8)

array_merge — ひとつまたは複数の配列をマージする

説明

array_merge(array ...$arrays): array

前の配列の後ろに配列を追加することにより、ひとつまたは複数の配列の要素をマージし、得られた配列を返します。

入力配列が同じキー文字列を有していた場合、そのキーに関する後に指定された値が、前の値を上書きします。しかし、配列が同じ添字番号を有していても値は追記されるため、このようなことは起きません。

入力配列の中にある数値添字要素の添字の数値は、結果の配列ではゼロから始まる連続した数値に置き換えられます。

パラメータ

arrays: マージしていく任意の数の配列のリスト。

戻り値

結果の配列を返します。引数なしで呼ばれた場合、空の array を返します。

変更履歴

バージョン	説明
7.4.0	この関数は、引数なしでも呼び出せるようになりました。このバージョンより前では、少なくともひとつの引数が必須でした。

例

例1 array_merge() の例

<?php
$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid", 4);
$result = array_merge($array1, $array2);
print_r($result);
?>

上の例の出力は以下となります。

Array
(
    [color] => green
    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => trapezoid
    [4] => 4
)

例2 簡単な array_merge() の例

<?php
$array1 = array();
$array2 = array(1 => "data");
$result = array_merge($array1, $array2);
?>

数値添字が振りなおされることに注意!

Array
(
    [0] => data
)

二番目の配列の要素を最初の配列に追加したい (最初の配列に存在する要素は上書きせず、添字も変更しない) 場合は、配列結合演算子 + を使います。

<?php
$array1 = array(0 => 'zero_a', 2 => 'two_a', 3 => 'three_a');
$array2 = array(1 => 'one_b', 3 => 'three_b', 4 => 'four_b');
$result = $array1 + $array2;
var_dump($result);
?>

最初の配列のキーはそのまま残ります。両方の配列に同じキーが存在する場合は最初の配列のものが残り、二番目の配列の内容は無視されます。

array(5) {
  [0]=>
  string(6) "zero_a"
  [2]=>
  string(5) "two_a"
  [3]=>
  string(7) "three_a"
  [1]=>
  string(5) "one_b"
  [4]=>
  string(6) "four_b"
}

例3 array_merge() で配列以外の型を扱う例

<?php
$beginning = 'foo';
$end = array(1 => 'bar');
$result = array_merge((array)$beginning, (array)$end);
print_r($result);
?>

上の例の出力は以下となります。

    Array
    (
        [0] => foo
        [1] => bar
    )

参考

array_merge_recursive() - 一つ以上の配列を再帰的にマージする
array_replace() - 渡された配列の要素を置き換える
array_combine() - 一方の配列をキーとして、もう一方の配列を値として、ひとつの配列を生成する
配列演算子

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User Contributed Notes 5 notes

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304

Julian Egelstaff ¶

15 years ago


In some situations, the union operator ( + ) might be more useful to you than array_merge.  The array_merge function does not preserve numeric key values.  If you need to preserve the numeric keys, then using + will do that.

ie:

<?php

$array1[0] = "zero";
$array1[1] = "one";

$array2[1] = "one";
$array2[2] = "two";
$array2[3] = "three";

$array3 = $array1 + $array2;

//This will result in::

$array3 = array(0=>"zero", 1=>"one", 2=>"two", 3=>"three");

?>

Note the implicit "array_unique" that gets applied as well.  In some situations where your numeric keys matter, this behaviour could be useful, and better than array_merge.

--Julian

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ChrisM ¶

2 years ago


I wished to point out that while other comments state that the spread operator should be faster than array_merge, I have actually found the opposite to be true for normal arrays. This is the case in both PHP 7.4 as well as PHP 8.0. The difference should be negligible for most applications, but I wanted to point this out for accuracy.

Below is the code used to test, along with the results:

<?php
$before = microtime(true);

for ($i=0 ; $i<10000000 ; $i++) {
    $array1 = ['apple','orange','banana'];
    $array2 = ['carrot','lettuce','broccoli'];
    
    $array1 = [...$array1,...$array2];
}

$after = microtime(true);
echo ($after-$before) . " sec for spread\n";

$before = microtime(true);

for ($i=0 ; $i<10000000 ; $i++) {
    $array1 = ['apple','orange','banana'];
    $array2 = ['carrot','lettuce','broccoli'];
    
    $array1 = array_merge($array1,$array2);
}

$after = microtime(true);
echo ($after-$before) . " sec for array_merge\n";
?>

PHP 7.4:
1.2135608196259 sec for spread
1.1402177810669 sec for array_merge

PHP 8.0:
1.1952061653137 sec for spread
1.099925994873 sec for array_merge

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Andreas Hofmann ¶

2 years ago


In addition to the text and Julian Egelstaffs comment regarding to keep the keys preserved with the + operator:
When they say "input arrays with numeric keys will be renumbered" they MEAN it. If you think you are smart and put your numbered keys into strings, this won't help. Strings which contain an integer will also be renumbered! I fell into this trap while merging two arrays with book ISBNs as keys. So let's have this example:

<?php
    $test1['24'] = 'Mary';
    $test1['17'] = 'John';

    $test2['67'] = 'Phil';
    $test2['33'] = 'Brandon';

    $result1 = array_merge($test1, $test2);
    var_dump($result1);

    $result2 = [...$test1, ...$test2];    // mentioned by fsb
    var_dump($result2);
?>

You will get both:

array(4) {
  [0]=>
  string(4) "Mary"
  [1]=>
  string(4) "John"
  [2]=>
  string(4) "Phil"
  [3]=>
  string(7) "Brandon"
}

Use the + operator or array_replace, this will preserve - somewhat - the keys:

<?php
    $result1 = array_replace($test1, $test2);
    var_dump($result1);

    $result2 = $test1 + $test2;
    var_dump($result2);
?>

You will get both:

array(4) {
  [24]=>
  string(4) "Mary"
  [17]=>
  string(4) "John"
  [67]=>
  string(4) "Phil"
  [33]=>
  string(7) "Brandon"
}

The keys will keep the same, the order will keep the same, but with a little caveat: The keys will be converted to integers.

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fsb at thefsb dot org ¶

4 years ago


We no longer need array_merge() as of PHP 7.4.

    [...$a, ...$b]

does the same as

    array_merge($a, $b)

and can be faster too.

https://wiki.php.net/rfc/spread_operator_for_array#advantages_over_array_merge

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JoshE ¶

2 years ago


Not to contradict ChrisM's test, but I ran their code example and I got very different results for PHP 8.0.

Testing PHP 8.0.14
1.4955070018768 sec for spread
4.4120140075684 sec for array_merge

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