- array_combine: documentation ( source)
- array_column: documentation ( source)
- var_export: documentation ( source)
- array_filter: documentation ( source)
- array_keys: documentation ( source)
<?php
$items = [
'a' => [],
'b' => ['id' => 'B'],
'c' => ['id' => 'C'],
'd' => [],
'e' => ['id' => 'E'],
];
var_export(
array_filter(
array_combine(
array_keys($items),
array_column($items, 'id'))));