Merging Associative Arrays and adding Missing Columns with Default Values

Merging multiple associative arrays while preserving all unique keys and adding missing columns with default values can be achieved using various techniques. Let's explore two methods to accomplish this:

Method 1: Using array_merge and RecursiveIterationIterator

$a = array('a' => 'some value', 'b' => 'some value', 'c' => 'some value');
$b = array('a' => 'another value', 'd' => 'another value', 'e' => 'another value', 'f' => 'another value');
$c = array('b' => 'some more value', 'x' => 'some more value', 'y' => 'some more value', 'z' => 'some more value');

$d = array($a, $b, $c);
$keys = array();

foreach (new RecursiveIteratorIterator(new RecursiveArrayIterator($d)) as $key => $val) {
    $keys[$key] = '';
}

$data = array();
foreach ($d as $values) {
    $data[] = array_merge($keys, $values);
}

echo '
';
print_r($data);
This approach first uses RecursiveIteratorIterator in conjunction with array_merge to identify all unique keys in each associative array. It then initializes an empty array ($keys) with the identified keys. Subsequently, it iterates through each array in $d, merging the $keys array with each array's values to obtain the desired format.
Method 2: Using array_combine and array_map
$keys = array_keys(call_user_func_array('array_merge', $d));
$key_pair = array_combine($keys, array_fill(0, count($keys), null));
$values = array_map(function ($e) use ($key_pair) {
    return array_merge($key_pair, $e);
}, $d);
This approach employs array_keys to determine the union of all unique keys in the merged array. It then utilizes array_combine to create a key-value pair where the keys are the unique keys, and the values are null. Finally, array_map is used to iterate through $d, merging the key-value pair ($key_pair) with each associative array in $d, resulting in the desired format.