createCardinality must return a Collection. I think the simplest way of
solving your problem is to write a simple class LetterCounter implementing
the counting and a DRL function extracting the collection of Tuples from the LetterCounter:

public class LetterCounter extends HashMap<Character,Integer> {
    public static  Set<Map.Entry<Character,Integer>> counterSet( Collection<Character> l ){
        return new LetterCounter( l ).entrySet();
    }
    public LetterCounter( Collection<Character> chars ){
        super();
        for( Character c: chars ){
            Integer count = get( c );
            put( c, count == null ? 1 : count + 1 );
        }
    }
}

rule "count"
when
    $t: Something( $l: collectionOfLetters )
    Map.Entry(  $key: key, $val: value > 1 ) from LetterCounter.counterSet( $l )
then
    System.out.println( "letter " + $key + ": " + $val );
end

-W

On 18 December 2010 12:16, AleBu <aleboo@gmail.com> wrote:

Hi,
I am new to Drools and do some experiments on it, and encountered on a
problem which can't solve for a last few days, so maybe someone can explain
what I am doing wrong?
I will probably explain my problem with example. Lets say we have a
collection of letters like 'a', 'b', 'c', 'a', 'd', 'e', 'c'. And I want to
report all letters that are duplicated, but only once providing a number of
duplication. In other words, for each letter which is duplicated I need to
do a report by saying 'Letter X is duplicated N times.
My idea was to create cardinality collection for letters which is a
collection of POJOs Tuple where first is letter and second is cound (first
and second are properties). I created a function for it createCardinality(
Collection letters ) which returns such cardinality info and tried something
like:
when
       Something( $letters: collectionOfLetters )
       Tuple( $letter: first, $count: second > 1 ) from collect( Tuple() from
createCardinality( $letters ) )
then
       System.out.println( "Letter "+letter+" is duplicated "+$count+"
times" )

But I am reported (at least it looks like this) about the problems with my
function createCardinality(). Maybe I misunderstood something about usage of
FROM?
--
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