関連ワード:  php check if element exists in array    php check if key exists in array    php check if value exists in array    php check if value exists in array of objects    php check if item exists in array    php check if element exists in associative array    php check if value exists in multidimensional array    php check if key exists in multidimensional array    php check if key exists in associative array    php check if value exists in associative array