How to filter an array by keys using another array

Question

I working now for a couple of hours on my project, i have some key's from a early array that i want to loop to my new array and pick the value of the key's that i have from the early array.

Early array:

$old_keys = ['key1','key2','key3'];

New array:

$result = ['key1' => 'foo', 'key2' => 'bar', 'key6' => 'ipsum'];

Output that i want is:

$output = ['foo', 'bar'];

This is what i made:

foreach ($old_keys as $old_key) {

    $output[] = array_column($result, $old_key);

}
return $output;

What did i wrong because everything what i get is a empty array

Thanks a lot!

Update:

$keys = array_flip($old_keys);

$output = array_values(array_intersect_key($result, $keys));

echo '<pre>';
var_dump($output);

The $output is now filled with the multidimensional array of $result, but the values 'foo' and 'bar' are in the second level of this multidimensional array. The problem is, i get only the first level of this array and not the second level.

example of the output:

[
 [0] => string
 [1] => string
 [
  [key1] => foo
  [key2] => bar
 ]
]

What i want is:

[
 [0] => string
 [1] => string
 [3] => foo
 [4] => bar
]

Solution:

$flat = iterator_to_array(new RecursiveIteratorIterator(new RecursiveArrayIterator($result)), true);

While you are still here, you may want to re-title your question, because it is not an accurate way to describe your process. — mickmackusa
– mickmackusa ♦, Commented Mar 17, 2017 at 2:28
perhaps something like: How to filter an array by keys using another array — mickmackusa
– mickmackusa ♦, Commented Mar 17, 2017 at 3:22

mickmackusa · Accepted Answer · 2017-03-17 01:49:34Z

1

Filter the $result array using $old_keys, but use the $old_keys values as keys:

$old_keys = array_flip(['key1','key2','key3']);
$result = ['key1' => 'foo', 'key2' => 'bar', 'key6' => 'ipsum'];
$output=array_intersect_key($result,$old_keys);
print_r($output);

If you want to re-index the keys in the result, replace the $output declaration with:

$output=array_values(array_intersect_key($result,$old_keys));

edited Mar 17, 2017 at 1:49

answered Mar 17, 2017 at 1:41

mickmackusa♦

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8 Comments

Pieter Dijkstra Over a year ago

Thanks, but i get so as i expect an empty array as output, because result is a multidimensional array.

mickmackusa Over a year ago

@PieterDijkstra In your question, $result is not a multidimensional array. Please update your question to present $result as a multidimensional array. You must offer me a correct sample to manipulate so I can replicate the issue and solve the problem.

mickmackusa Over a year ago

I don't know if I need to explain this bit, but my code replaces yours. You don't need to do any looping. And you can just return the print_r value. If there are no old keys in the result array, output will be an empty array.

Pieter Dijkstra Over a year ago

see my update, i've already update my code with yours but it doesn't work on the way i want.

mickmackusa Over a year ago

Something else must be wrong with your code, because this works: sandbox.onlinephpfunctions.com/code/…

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