Re: [rules-users] finding matching entries in parallel arrays
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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