[rules-users] finding matching entries in parallel arrays

[Mark Proctor]

inside of a pattern == is in equality. Inside of an eval it all depends 
if you are using the java or mvel dialect - its just an expression, so 
it obeys the host expression language.

Mark
Aaron Dixon wrote:
> The "from" conditional element solves part of my problem:
>
> rule "Find matching entry in parallel arrays (alternate)"
>     when
>         $first : ArrayList( )
>         $second : ArrayList( this != $first )
>         $fi : Object() from $first
>         $si : Object() from $second
>         eval( $fi == $si )
>     then
>         System.out.println ( " Found match at index ? : " + $fi + "!" );
> end
>
> I do want reference equality (==) in my eval. But I understand that 
> object equality would look just like:
>
> eval( $fi .equals( $si ) )
>
>
> Thanks!
>
> Aaron
>
>
> On 8/7/07, *Mike D* <mike.dalaker at kewill.com 
> <mailto:mike.dalaker at kewill.com>> wrote:
>
>
>     Mark,
>
>     Just to be sure I read this correctly:
>
>     eval( $fi == $si )
>
>     means it's checking objects, not values within the object?
>     If a compare of values is needed, another eval would have to be
>     written to
>     compare temp value.
>
>     Thanks,
>     Mike
>
>
>     Oh, and can we change the documenatation examples please?
>
>     Somthing like...
>
>     rule
>         when
>             Team( $team : name == "ManU" )
>             $person : Person( favouriteTeam == $team )
>         then
>             System.out.println( $person.getName() + " likes Manchester" );
>         end
>
>     rule
>         when
>             Team( $team : name == "Chelsea" )
>             $person : Person( favouriteTeam != $team )
>         then
>             System.out.println( $person.getName() + " does not like
>     Chelsea at
>     all" );
>         end
>
>
>
>     Mark Proctor wrote:
>     >
>     > We don't really recommend you assert ArrayLists etc as facts, as
>     they
>     > have no contextual meaning
>     >
>     > $first : ArrayList( )
>     > $second : ArrayList( this != $first )
>     > $fi Object() from $first
>     > $si Object from $second
>     > eval( $fi == $si )
>     >
>     > 'from' allows iteration of lists, so you could potentially do it
>     this
>     > way, although it doesn't provide an index number for you.... You
>     could
>     > possibly have a global that as part of a function in eval get
>     > incremented and that global is available in the consequence. But
>     you'll
>     > have to be very careful with concurrency.... Might be easier to
>     have a
>     > hashmap of indexes where the key is made up of $first and
>     $second. Btw
>     > == checks for same instances, not an equality check, is that
>     what you
>     > wanted?
>     >
>     > Mark
>     >
>     > Aaron Dixon wrote:
>     >> My problem boils down to finding matching entries in parallel
>     arrays.
>     >>
>     >> Here is a rule that succesfully does just that:
>     >>
>     >> rule "Find matching entry in parallel arrays"
>     >>     when
>     >>         $first : ArrayList( )
>     >>         $second : ArrayList( this != $first )
>     >>         $i : Integer( this < $first.size )
>     >>         eval( $first.get($i) == $second.get($i) )
>     >>     then
>     >>         System.out.println ( "Found match at index " + $i + "!" );
>     >> end
>     >>
>     >>
>     >> To execute this rule, I must insert (assert) the two ArrayList
>     facts
>     >> as well as at least as many Integer facts as there are items in the
>     >> ArrayLists.
>     >>
>     >> What I don't like about this rule is that
>     >>
>     >>     (1) I have to assert the Integers
>     >>     (2) I can't support arbitrarily-sized lists in my rules
>     (without
>     >> asserting that many Integer facts)
>     >>
>     >> So -- Is there a better way?
>     >>
>     >> What if a future version of Drools supported implicit Number facts
>     >> that allowed for these kinds of indexing rules?
>     >>
>     >> Aaron
>     >>
>     >>
>     >>
>     >>
>     >>
>     ------------------------------------------------------------------------
>     >>
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>     >>
>     >
>     >
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