Merge one column from two 2d arrays and remove duplicates

Question

I am running two queries, they return arrays similar to what is shown below:

First:

array(
    array(
        'id' => 1
    ),
    array(
        'id' => 2
    ),
    array(
        'id' => 3
    ),
    array(
        'id' => 4
    ),
)

Second:

array(
    array(
        'id' => 4
    ),
    array(
        'id' => 5
    ),
    array(
        'id' => 6
    ),
    array(
        'id' => 7
    ),
)

But I want to end up with

$ids = array(1,2,3,4,5,6,7);

But the only way I can think of to do that is

$ids = array();
foreach(array($array1, $array2) as $a){
    foreach($a as $id){
        $ids[] = $id['id'];
    }
}
$ids = array_unique($ids);

But that doesn't seem very efficient to me, and with the wealth of array functions out there, I am wondering if there is a better way?

Answer 1

There would be a few ways to handle this. I think I would probably start with array_merge() on the two original arrays, then flatten it with array_map(), and finally call array_unique().

// Combine them
$new = array_merge($array1, $array2);
// Flatten them
// array_map() is used to select the 'id' key from each
$new = array_map(function($a) { 
  return $a['id'];
}, $new);
// And get the unique values
$ids = array_unique($new);

print_r($ids);
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [5] => 5
    [6] => 6
    [7] => 7
)

Better: Do it in one query.

After seeing the query, these do not need to be two arrays. It can be done with a single UNION query. Using a plain UNION instead of a UNION ALL will deduplicate them for you.

SELECT
  game_id AS id
FROM user_game 
WHERE user_id = :userid
UNION
SELECT
  id
FROM games
WHERE referee_id = :userid OR reviewer_id = :userid
ORDER BY id

When fetching rows, since you have only one column, you may consider directly flattening it in the fetch.

// For example
while ($row = $stmt->fetch()) {
  // Pluck only the id from the row fetched
  $ids[] = $row['id'];
}
// $ids is now a 1D array.