unique_mapping() - create a mapping from an array based on a function

mapping unique_mapping( mixed *arr, string fun, object ob,
                          mixed extra, ... );
mapping unique_mapping( mixed *arr, function f, mixed extra, ... );

Returns a mapping built in the following manner:

'ob->fun()' or 'f' is evaluated for each member of the array.  The mem‐
bers for  which  the  function  returns  the  same  value  are  grouped
together, and associated with the return value as the key.

The  key/value  ordering  in the returned mapping is consistent but not
guaranteed to not change in the future.

filter_array(3), sort_array(3), map(3)