Counting and Grouping Strings in Drools Expert 6.5, with accumulate or collect keyword

How to compute the percentage of Vs in a list with drools rules. In case of percentage of V are 80%, then fire a drools rule.

I have a ArrayList that will have only two values: V and N.

List<String> list = new ArrayList<>();

How to count the number of V with drools rules, every V and N will worth 1, get total sum sum of V and N.

In java

  Map<String, Long> counted = list.stream()
             .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
    System.out.println("Counted: "+counted);

The expression above prints

Counted: {V=4, N=15}

After get the the values, there will be an drols rule expression, which in case of 80 % occurrence the count V appearance prints "ok" otherwise prints not allowed.

Solution

Here is a rule that computes the percentage of Vs in the list:

rule "countVN"
when
  $vn: ArrayList( $s: size )
  accumulate( String( toString == "V" ) from $vn;
              $cnt: count( 1 );
              $cnt.doubleValue()/$s >= 0.8 )
then
  System.out.println( "80% or more" );
end

This fires just for the >= 80% case. If you need a result in any case, use

  ...
  accumulate( String( toString == "V" ) from $vn;
              $cnt: count( 1 ))
then
  if( $cnt.doubleValue()/$s >= 0.8 ) ...