从另一个数组的键中提取数组值的最简单方法是什么

Question

I have two arrays:

$array1 = [1,2,3,4,5,6,7,8,9];
$array2 = [0,1,2,3];

I want to assign the values from the first array to another array according to the values from the second array as keys. So instead of doing it one by one like this:

$array3 = [$array1[$array2[0]],$array1[$array2[1]],$array1[$array2[2]],$array1[$array2[3]]];

I tried to do it like this:

$array3 = [$array1[$array2]];

But I got the following error:

Warning: Illegal offset type

What I want to get is:

Array ( [0] => 1 [1] => 2 [2] => 3  [3] => 4 )

Any ideas what is the right way to do it?

Answer 1

There are probably numerous ways to solve this. Probably the simplest is to loop over the second array and add the corresponding values from the first into the new array...

$array3 = [];
foreach ( $array2 as $extract ) {
    $array3[] = $array1 [ $extract ];
}
print_r($array3);

Answer 2

I found a short way:

array_map(function($x) use ($array1) { return $array1[$x]; }, $array2);

Answer 3

A simple foreach loop should do the trick. Loop over second array and check if its key is set in the first array. If so, add to result, else skip.

$array1 = [1, 2, 3, 4, 5, 6, 7, 8, 9];
$array2 = [0, 1, 2, 3];

$result = [];

foreach ($array2 as $value) {
    if (isset($array1[$value])) {
        $result[] = $array1[$value];
    }
}

print_r($result);

Answer 4

From PHP7.4 you can use arrow function syntax and avoid the use() declaration. If you don't want to call any custom functions and don't want a classic loop, you can make 3 native function calls to generate an indexed array of results.

Code: ( Demo )

$array1 = [1, 2, 3, 4, 5, 6, 7, 8, 9];
$array2 = [3, 4];

var_export(
    array_values(array_intersect_key($array1, array_flip($array2)))
);
// array ( 0 => 4, 1 => 5, )

var_export(
    array_map(fn($v) => $array1[$v], $array2)
);
// array ( 0 => 4, 1 => 5, )