Return the new Map that swap key and value.
Return the new Map that swap key and value. If the several key is bound to one value, the result is unknown
Find a key which corresponds value and return the wrapped value or None.
Find a key which corresponds value and return the wrapped value or None. If the number of key >= 1, It is unspecified that which key is selected.
Return a Seq consist of found values.
Return a Seq consist of found values. Values ordering follows keys ordering.