Re: [rules-users] how to do things like "distinct"?
On 1 June 2011 16:55, Simon Chen <simonchennj(a)gmail.com> wrote:
Hi all,
I have the following problem.
Let's say, I have a class Number3(), with three fields a, b, and c.
I have the following rule:
rule "test3"
when
Number3($a: a, $b: b)
$minvalue: Number()
from accumulate(Number3(a == $a, b == $b, $c: c), min($c))
then
System.out.println($a + " " + $b + " " + $minvalue);
end
Say, I have four objects (1,2,3), (1,2,4), (1,3,4), (1,3,5).
The result shows four lines:
1 3 4.0
1 3 4.0
1 2 3.0
1 2 3.0
But I want the output to be:
1 3 4.0
1 2 3.0
meaning that for each unique pair of a and b, I want the rule to fire only
once.
In this particular case you might try
rule "test3"
when
Number3($a: a, $b: b, $c)
not Number3( a == $a, b == $b, c < $c )
then
System.out.println($a + " " + $b + " " + $c);
end
Event this will fail, if there are two identical (w.r.t. a, b and c) Number3
objects.
For the general case, you must have some way of picking a single Number3
with some a/b-combination.
Alternatively, insert possibly multiple triplets <a,b,min(c)> and harvest
one from each group, using additional rules.
Or use an additional fact containing <a,b(,c)> to indicate that you have
computed the minimum. But then you must get rid of these auxiliaries.
-W
Is this doable?
Thanks.
-Simon
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