Filter a flat associative array to only keep elements where related keys share the same suffix

I have a dynamic array as

[
    "question" => "test 1",
    "question1" => "hello test 1",
    "question2" => "hello test 2 checked",
    "homepage2" => "homepage",
    "question3" => "3 test checked",
    "homepage3" => "homepage",
    "question4" => "question 4 ? checked",
]

keys are "question", "question1"...etc and "homepage","homepage1"..etc so i want to display only the values from the array when the index is question($number) and has similar key as homepage($number)

How to make it look like the following?

[
    "question2" => "hello test 2 checked",
    "homepage2" => "homepage",
    "question3" => "3 test checked",
    "homepage3" => "homepage",
]

You could first create an array keyed by the suffix numbers, and store as value an array of all key/value pairs where the key has that suffix number. Then you would filter those that have two such key/value pairs, and arrange those in the format you need:

$arr = [
  "question"=> "test 1",
  "question1"=> "hello test 1",
  "question2"=> "hello test 2 checked",
  "homepage2"=> "homepage",
  "question3"=> "3 test checked",
  "homepage3"=> "homepage",
  "question4"=> "question 4 ? checked",
];

$temp = [];
foreach($arr as $key => $value) {
    if (preg_match("/^(question|homepage)(\d+)$/", $key, $parts))
        $temp[$parts[2]][$parts[0]] = $value;
}
$result = [];
foreach($temp as $num => $pair) {
    if (count($pair) == 2) $result = array_merge($result, $pair);
}

print_r($result);

$result will be:

Array (
    "question2" => "hello test 2 checked",
    "homepage2" => "homepage",
    "question3" => "3 test checked",
    "homepage3" => "homepage"
)

See it run on eval.in.

More logical structure

I would however suggest the more logical structure where you group question and homepage together in a pair (array), and assign that to a key which is the number of that pair. In that case the two loops need minor changes:

$temp = [];
foreach($arr as $key => $value) {
    if (preg_match("/^(question|homepage)(\d+)$/", $key, $parts))
        $temp[$parts[2]][$parts[1]] = $value;
}
$result = [];
foreach($temp as $num => $pair) {
    if (count($pair) == 2) $result[$num] = $pair;
}

This will give the following structure:

Array(
    "2" => Array(
        "question" => "hello test 2 checked",
        "homepage" => "homepage"
    ),    
    "3" => Array(
        "question" => "3 test checked",
        "homepage" => "homepage"
    )
)

See it run on eval.in.