[rules-users] How to use a result of custom defined function in WHEN part?

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? -- View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/How-to-use-a-result-o... Sent from the Drools - User mailing list archive at Nabble.com.