PHP array_merge with numerical keys

问题:

How can make it so array_merge() overwrites two keys with different values but same key index from two arrays?

for example, merging:

[0] => 'whatever'

with

[0] => 'whatever', [1] => 'a', [2] => 'b'

should produce

[0] => 'whatever', [1] => 'a', [2] => 'b'

Basically I want array_merge to bahave the same way it behaves if the arrays have string keys...

回答1:

Use the + operator.

Compare array_merge to + operator:

<?php

$a1 = array(0=>"whatever",);
$a2 = array(0=>"whatever",1=>"a",2=>"b");

print_r(array_merge($a1,$a2));
print_r($a1+$a2);
?>

Output:

Array
(
    [0] => whatever
    [1] => whatever
    [2] => a
    [3] => b
)
Array
(
    [0] => whatever
    [1] => a
    [2] => b
)

The + operator still works if your associative array has the numerical keys out-of-order:

<?php

$a1 = array(0=>"whatever",);
$a2 = array(1=>"a",0=>"whatever",2=>"b");

print_r(array_merge($a1,$a2));
print_r($a1+$a2);
?>

Output:

Array
(
    [0] => whatever
    [1] => a
    [2] => whatever
    [3] => b
)
Array
(
    [0] => whatever
    [1] => a
    [2] => b
)

Notice array_merge in this case creates a new key. Not desirable...

回答2:

Pretty easy to write manually:

function array_merge_custom($first, $second) {
    $result = array();
    foreach($first as $key => $value) {
        $result[$key] = $value;
    }
    foreach($second as $key => $value) {
        $result[$key] = $value;
    }

    return $result;
}

Update: This behaves differently than the union operator (return $first + $second;) because in this case the second array wins when both have elements with the same key.

However, if you switch the places of the arguments and place the array that you want to "win" in case of conflicts as the first operand, you can get the same behavior. So the function above behaves exactly like return $second + $first;.

回答3:

array_replace does exactly this. See: http://php.net/manual/de/function.array-replace.php

回答4:

function array_merge_custom()
{
    $array      = array();
    $arguments  = func_num_args();
    foreach($arguments as $args)
        foreach($args as $key => $value)
            $array[$key] = $value;
    return $array;
}

回答5:

You should use $a2+$a1 to get same result with array_merge($a1,$a2);

$a1 = array(
    'k1' => 1,
    'k2' => 2,
    'k3' => 3,
);

$a2 = array(
    'k1' => 11,
    'k2' => 22,
    'k4' => 44,
);

Code:

print_r(array_merge($a1,$a2));

Output:

Array ( 
    [k1] => 11 
    [k2] => 22 
    [k3] => 3 
    [k4] => 44 
)

Code:

print_r($a1+$a2);

Output:

Array ( 
    [k1] => 1 
    [k2] => 2 
    [k3] => 3 
    [k4] => 44 
)

Code:

print_r($a2+$a1);

Output:

Array ( 
    [k1] => 11 
    [k2] => 22 
    [k4] => 44 
    [k3] => 3 
) 

回答6:

You could use array_merge() and then use array_unique().

回答7:

the solution could be this:
function array_merge_custom($array1, $array2) {
    $mergeArray = [];
    $array1Keys = array_keys($array1);
    $array2Keys = array_keys($array2);
    $keys = array_merge($array1Keys, $array2Keys);

    foreach ($keys as $key) {
        $mergeArray[$key] = array_merge_recursive(isset($array1[$key]) ? $array1[$key] : [], isset($array2[$key]) ? $array2[$key] : []);
    }

    return $mergeArray;
}

$array1 = [
    '66_' => [
        'k1' => 1,
        'k2' => 1,
    ],
    '67_' => [
        'k1' => 1,
        'k2' => 1,
    ],
    '68_' => [
        'k1' => 1,
        'k2' => 1,
    ],
    68 => [
        'k1' => 1,
        'k2' => 1,
    ]
];
$array2 = [
    '66_' => [
        'a1' => 1,
        'a2' => 1,
    ],
    '68_' => [
        'b1' => 1,
        'b2' => 1,
    ],
    68 => [
        'b1' => 1,
        'b2' => 1,
    ]
];
echo '<pre>';
print_r(array_merge_custom($array1, $array2));

回答8:

$arrA = [10, 11, 12];
$arrB = [12, 13];

$arrCommon = array_keys(array_flip($arrA) + array_flip($arrB));

print_r($arrCommon);
Array
(
    [0] => 10
    [1] => 11
    [2] => 12
    [3] => 13
)

Compare to WRONG use of "+"

$arrCommon = $arrA + $arrB;

print_r($arrCommon);
Array
(
    [0] => 10
    [1] => 11
    [2] => 12
)