[gecode-users] iterating/filtering IntView

[Christian Schulte]

Just some additions to what Guido and Mikael said.

1. As you are in a propagator, you are talking about views - say of type
View - so you should use
   ViewValues<View> to iterate over the values.

2. The most efficient version is to create an iterator class that produces
the values you want
   to have for x1:
	- constructor: creates an iterator i for x1
	- operator(), test whether iterator is done: check whether i is done
	- operator++, move to next value:
		do 
		  ++i;
		while (i() && !my_predicate(x0.val(),i.val()));
      - value access val(): just return i.val();

3. Then turn the value iterator from above into a range iterator with
Iter::Values::ToRanges, let's call it r

4. Then tell that the values of x1 must be r:
	x1.narrow(home,r);
	Note, that this is safe: narrow has acopying semantics: it first
reads all of r (depending on x1)
	and only then updates the domain of x1.

For an example see gecode/int/element/int.icc or just grep for
Values::ToRanges

Christian 

--
Christian Schulte, http://www.imit.kth.se/~schulte/ 

-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Kilian Sprotte
Sent: Monday, May 14, 2007 8:16 PM
To: users at gecode.org
Subject: [gecode-users] iterating/filtering IntView


Hi,

I am inside a propagate method of a binary propagator... :)

At some point, I know that x0 is assigned. What I would like to do is  
to filter the domain of x1 using a given predicate function.

if (x0.assigned()) {
    IntVarValues r1(x1);
    while (r1()) {
      if (!my_predicate(x0.val(), r1.val()))
        GECODE_ME_CHECK(x1.nq(home, r1.val()))
      ++r1;
    }
    return ES_SUBSUMED;

It does not seem to be a good idea however to alter the view x1 while  
iterating over it...(is it true that this should not be done/will  
cause problems?)

Hhm, could anyone give me a hint, what I could use in order to do  
this safely?

Thanks a lot,
   Kilian


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