When you want to allow only certain keys in your arrays, especially when the array comes from request parameters, you can use array_intersect_key together with array_flip.
$parameters = ['foo' => 'bar', 'bar' => 'baz', 'boo' => 'bam'];$allowedKeys = ['foo', 'bar'];$filteredParameters = array_intersect_key($parameters, array_flip($allowedKeys));// $filteredParameters contains ['foo' => 'bar', 'bar' => 'baz]If the parameters variable doesn’t contain any allowed key, then the filteredParameters variable will consist of an empty array.
Since PHP 5.6 you can use array_filter for this task too, passing the ARRAY_FILTER_USE_KEY flag as the third parameter:
$parameters = ['foo' => 1, 'hello' => 'world'];$allowedKeys = ['foo', 'bar'];$filteredParameters = array_filter($parameters,function ($key) use ($allowedKeys) {return in_array($key, $allowedKeys);},ARRAY_FILTER_USE_KEY);Using array_filter gives the additional flexibility of performing an arbitrary test against the key, e.g. $allowedKeys could contain regex patterns instead of plain strings. It also more explicitly states the intention of the code than array_intersect_key() combined with array_flip().