For example
$users = array(
array(
'userid' => '100',
'name' => 'Sandra Shush',
),
array(
'userid' => '5465',
'name' => 'Stefanie Mcmohn',
),
array(
'userid' => '40489',
'name' => 'Michael',
)
); $key = array_search(40489, array_column($users, 'uid')); 