如何合并缺少列的关联数组并提供默认值？

合并缺少列和默认值的关联数组

给定一个关联数组数组，任务是将它们组合起来，合并数组键并填充缺少的列使用默认值。

<code class="php">$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);</code>

var_export($d)

将输出：

array (
  0 =>
  array (
    'a' => 'some value',
    'b' => 'some value',
    'c' => 'some value',
  ),
  1 =>
  array (
    'a' => 'another value',
    'd' => 'another value',
    'e' => 'another value',
    'f' => 'another value',
  ),
  2 =>
  array (
    'b' => 'some more value',
    'x' => 'some more value',
    'y' => 'some more value',
    'z' => 'some more value',
  ),
)

所需的输出是：

Array
(
    [0] => Array
        (
            [a] => some value
            [b] => some value
            [c] => some value
            [d] =>
            [e] =>
            [f] =>
            [x] =>
            [y] =>
            [z] =>
        )

    [1] => Array
        (
            [a] => another value
            [b] =>
            [c] =>
            [d] => another value
            [e] => another value
            [f] => another value
            [x] =>
            [y] =>
            [z] =>
        )

    [2] => Array
        (
            [a] =>
            [b] => some more value
            [c] =>
            [d] =>
            [e] =>
            [f] =>
            [x] => some more value
            [y] => some more value
            [z] => some more value
        )
)

要实现此目的， array_merge()可以使用。

<code class="php">$keys = array();
foreach(new RecursiveIteratorIterator(new RecursiveArrayIterator($d)) as $key => $val) $keys[$key] = '';
$data = array();
foreach($d as $values) {
    $data[] = array_merge($keys, $values);
}
echo '<pre class="brush:php;toolbar:false">';
print_r($data);</code>

另一种方法是创建密钥对值，然后映射每个 $d 并合并。

<code class="php">$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);</code>

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