Without any conditions and constraints, this is just a simple computation
you could code in Java and invoke in some appropriate place. But I
suspect you haven't told us the whole story...

You don't say where this "list" is; so I assume it's a field in some other fact.

This code is absolutely untested.

rule count
when
    ListHolder( $list : list )
    $map: Map from accumulate ( XXX( $id: id, $type: type ) from $list,
          init( Map map = new HashMap(); ),
          action( Integer count = map.get( $type );
                       count = Integer.valueOf( count == null ? 1 : count+1 );
                       map.put( $type, count ); ),
result( map ) )
then
   // ... use $map
end

-W

2010/11/5 Yaniv Itzhaki <iyaniv@gmail.com>

Hi All,

I need to go over a not distinct list and count distinct each element in the list.

for example:

Object XXX {
int id;

String type;
}

XXX:
id type
1 A
2 B
3 A
4 C
5 C

The rule should be activated per type and give as a result the count of each type:

A 2
B 1
C 2

Thanks

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