Get values of array using as key values of another array

Question

I have an array with some values (numeric values):

$arr1 = [1, 3, 8, 12, 23]

and I have another associative array that a key (which matches to a value of $arr1) correspond to a value. This array may contain also keys that don't match with $arr1.

$arr2 = [1 => "foo", 2 => "foo98", 3 => "foo20", 8 => "foo02", 12 => "foo39", 15 => "foo44", 23 => "foo91", 34 => "foo77"]

I want as return the values of $arr2 specifying as key the values of $arr1:

["foo", "foo20", "foo02", "foo39", "foo91"]

If possible, all this, without loops, using just PHP array native functions (so in an elegant way), or at least with the minimum number of loops possible.

Whether you can see the 'loops' or not, they will be there. So this cannot be done without 'looping' somehow. — KIKO Software
– KIKO Software, Commented May 5, 2019 at 13:00

dWinder · Accepted Answer · 2019-05-05 13:02:33Z

3

Minimal loop is simple - 1. as:

foreach($arr1 as $k) {
    $res[] = $arr2[$k];
}

You can do that with array_walk but I think this simple way is more readable.

If you insist you can do with array_filter + array_values + in_array as:

$res = array_values(array_filter($arr2,
    function ($key) use ($arr1) { return in_array($key, $arr1);},
    ARRAY_FILTER_USE_KEY
));

You can see this for more about filtering keys

edited May 5, 2019 at 13:02

answered May 5, 2019 at 13:01

dWinder

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1 Comment

KIKO Software Over a year ago

I agree with that sentiment.

Nigel Ren · Accepted Answer · 2019-05-05 13:19:29Z

To do it purely with array functions, you could do it as...

print_r(array_intersect_key($arr2, array_flip($arr1) ));

So array_flip() turns the items you want form the array into the keys for $arr1 and then uses array_intersect_key() to match the keys with the main array and this newly created array.

Gives...

Array
(
    [1] => foo
    [3] => foo20
    [8] => foo02
    [12] => foo39
    [23] => foo91
)

If you don't want the keys - add array_values() around the rest of the calls...

print_r(array_values(array_intersect_key($arr2, array_flip($arr1) )));

to get

Array
(
    [0] => foo
    [1] => foo20
    [2] => foo02
    [3] => foo39
    [4] => foo91
)

Although as pointed out - sometimes a simple foreach() is just as good and sometimes better.

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