php array_merge 和 array + array 有什么区别？

What's the difference between array_merge and array + array?

提问by The Pixel Developer

A fairly simple question. What's the difference between:

一个相当简单的问题。有什么区别：

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

and

和

$merged = $array1 + $array2;

?

?

采纳答案by Mike Lewis

The difference is:

区别在于：

The +operator takes the union of the two arrays, whereas the array_mergefunction takes the union BUTthe duplicate keys are overwritten.

该+操作需要两个数组的工会，而array_merge函数需要工会BUT的重复键被覆盖。

回答by Yehosef

Here's a simple illustrative test:

这是一个简单的说明性测试：

$ar1 = [
   0  => '1-0',
  'a' => '1-a',
  'b' => '1-b'
];


$ar2 = [
   0  => '2-0',
   1  => '2-1',
  'b' => '2-b',
  'c' => '2-c'
];

print_r($ar1+$ar2);

print_r(array_merge($ar1,$ar2));

with the result:

结果：

Array
(
  [0] => 1-0
  [a] => 1-a
  [b] => 1-b
  [1] => 2-1
  [c] => 2-c
)
Array
(
  [0] => 1-0
  [a] => 1-a
  [b] => 2-b
  [1] => 2-0
  [2] => 2-1
  [c] => 2-c
)

Notice that duplicate non-numeric keys will take the first value using the union operator but the later one using the array_merge.

请注意，重复的非数字键将使用联合运算符取第一个值，但使用 array_merge 取后一个值。

For numeric keys, the first value will be used with the union operator whereas the all the values will be used with the array_merge, just reindexed.

对于数字键，第一个值将与联合运算符一起使用，而所有值将与 array_merge 一起使用，只是重新索引。

I generally use union operator for associative arrays and array_merge for numeric. Of course, you can just as well use the array_merge for associative, just that the later values overwrite earlier ones.

我通常对关联数组使用联合运算符，对数字使用 array_merge。当然，您也可以使用 array_merge 进行关联，只是后面的值会覆盖前面的值。

回答by BoltClock

array_merge()causes all numeric keys found in the input arrays to be reindexed in the resultant array. The union operator +does not cause a reindex.

array_merge()导致在输入数组中找到的所有数字键在结果数组中重新索引。联合运算符+不会导致重新索引。

回答by luchaninov

Source: https://softonsofa.com/php-array_merge-vs-array_replace-vs-plus-aka-union/

来源：https: //softonsofa.com/php-array_merge-vs-array_replace-vs-plus-aka-union/

Stop using array_merge($defaults, $options):

停止使用 array_merge($defaults, $options)：

function foo(array $options)
{
   $options += ['foo' => 'bar'];

   // ...
}

Note: array_replace function exists since PHP5.3.

注意：array_replace 函数从 PHP5.3 开始存在。

回答by Tschallacka

The + sign only takes the value from the firstoccurence of an array key.
array_merge takes the value from the lastoccurrence of an array key.

+ 号只取数组键第一次出现时的值。
array_merge 从最后一次出现的数组键中获取值。

Example:

例子：

$first = ['a'=>'one',
        'b'=>'two',
        'c'=>'three'];

$second = ['a'=>'fourth',
        'b'=>'fifth',
        'c'=>'sixth',
        '3'=>'number three'];

$merged = $first + $second;
echo "<pre> plus sign merge\n";
var_dump($merged);

$merged = array_merge($first,$second);
echo "\n array_merge function merge\n";
var_dump($merged);

This outputs:

这输出：

plus sign merge
array(4) {
["a"]=>
string(3) "one"
["b"]=>
string(3) "two"
["c"]=>
string(5) "three"
[3]=>
string(12) "number three"
}

array_merge function merge
array(4) {
["a"]=>
string(6) "fourth"
["b"]=>
string(5) "fifth"
["c"]=>
string(5) "sixth"
[0]=>
string(12) "number three"
}

加号合并
数组(4) {
["a"]=>
string(3) "one"
["b"]=>
string(3) "two"
["c"]=>
string(5) "three"
[3]=>
字符串（12）“数字三”
}

array_merge function merge
array(4) {
["a"]=>
string(6) "fourth"
["b"]=>
string(5) "fifth"
["c"]=>
string(5) "sixth"
[0]=>
字符串（12）“数字三”
}

Interesting to note in this is that the array_mergeactally erasesthe '3' index of number three even though it's a string, because it's a number.

有趣的是，尽管它是一个字符串，但array_merge实际上删除了数字 3 的 '3' 索引，因为它是一个数字。

So take care when merging with array_mergearrays with numerical indexes. They might lose their keys. if they are important to you precede them with a string.

因此，在与array_merge具有数字索引的数组合并时要小心。他们可能会丢失钥匙。如果它们对您很重要，请在它们前面加上一个字符串。

so instead of '3' => 'three'use something like '_3' => 'three'

所以而不是'3' => 'three'使用类似的东西'_3' => 'three'

回答by klennepette

I believe array_mergeoverwrites duplicate non_numeric keys while $array1 + $array2does not.

我相信会array_merge覆盖重复的非数字键，而$array1 + $array2不会。

回答by jacek.ciach

Yet another example (arrays without explicit keys; it's obvious regarding to how the operator +and array_mergework, but "obvious" things are simpler when seen ;))

另一个例子（没有显式键的数组；关于运算符+和array_merge工作的方式很明显，但是“显而易见”的事情在看到时更简单;))

$a = array('apple');
$b = array('orange', 'lemon');

echo '$a + $b = ';             print_r($a + $b);
echo 'array_merge($a, $b) = '; print_r(array_merge($a, $b));

will give:

会给：

$a + $b = Array
(
    [0] => apple
    [1] => lemon
)
array_merge($a, $b) = Array
(
    [0] => apple
    [1] => orange
    [2] => lemon
)

回答by Nedyalko Dyakov

So apparently if you change the order both union and merge will do the same thing

所以很明显，如果你改变顺序， union 和 merge 都会做同样的事情

$a = array('foo' => 'bar', 'x' => 'fromA');
$b = array('foo' => null, 'x' => 'fromB');

echo '$a+$b: ';
var_dump($a+$b);

echo '$b+$a: ';
var_dump($b+$a);

echo 'array_merge($a, $b): ';
var_dump(array_merge($a, $b));

echo 'array_merge($b, $a): ';
var_dump(array_merge($b, $a));

Outputs :

输出：

$a+$b: array(2) {
  ["foo"]=>
  string(3) "bar"
  ["x"]=>
  string(5) "fromA"
}
$b+$a: array(2) {
  ["foo"]=>
  NULL
  ["x"]=>
  string(5) "fromB"
}
array_merge($a, $b): array(2) {
  ["foo"]=>
  NULL
  ["x"]=>
  string(5) "fromB"
}
array_merge($b, $a): array(2) {
  ["foo"]=>
  string(3) "bar"
  ["x"]=>
  string(5) "fromA"
}

Keep in mind the order of the arrays.

请记住数组的顺序。

回答by ZalemCitizen

Please pay attention for another difference: the union (+) won't overwrite non-empty value with empty value (considering a same key), whereas array_merge will:

请注意另一个区别：联合 (+) 不会用空值覆盖非空值（考虑相同的键），而 array_merge 将：

$a = array('foo' => 'bar');
$b = array('foo' => ''); // or false or 0

print_r($a+$b);
print_r(array_merge($a, $b);

Outputs :

输出：

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