Hi, Mattias, your solution works because Amos' algo was a special case where you can verify the path simply by looking one step back. It's a smart solution to his problem!
However, what about traversals where you have more complex calculations going on and essentially want to carry a state along with you from hop to hop. That state would be different for each traversal branch. Is that something the traversal API should support? Community, WDYT? (sorry for thread hijack) David On Thu, Dec 23, 2010 at 12:48 PM, Mattias Persson <matt...@neotechnology.com > wrote: > Hi, interesting traversal... so you're saying that paths like this could be > returned: > > (start)-B->()-A[P=1]->()-A[P=1]->()-B->(end) > > but not paths like this: > > (start)-A[P=1]->()-B->()-A[P=2]->(end) > > am I correct? There are common path algorithms in > GraphAlgoFactory< > http://components.neo4j.org/neo4j-graph-algo/apidocs/org/neo4j/graphalgo/GraphAlgoFactory.html > >but > they don't support an evaluator as an argument, an evaluator which > could > look like: > > { > public Evaluation evaluate( Path position ) > { > Relationship rel = position.lastRelationship(); > if ( rel == null || !rel.isType( MyRelTypes.A ) ) > return Evaluation.INCLUDE_AND_CONTINUE; > > Object p = rel.getProperty( "P" ); > Object previousP = lookBackwardsForP( position ); > if ( previousP != null && !p.equals( previousP ) ) > return Evaluation.EXCLUDE_AND_PRUNE; > return Evaluation.INCLUDE_AND_CONTINUE; > } > > private Object lookBackwardsForP( Path position ) > { > int count = 0; > for ( Relationship rel : position.relationships() ) > { > // Skip the first one > if ( count++ > 0 ) > { > if ( rel.isType( MyRelTypes.A ) ) > return rel.getProperty( "P" ); > } > } > return null; > } > } > > You could probably create a breadth first traverser with such an evaluator > to get your paths. I don't know about performance since each evaluation > needs to go back one or more steps in the path, but you could try it out. > > 2010/12/23 Amos Ben Israel <lucis.domi...@gmail.com> > > > Hello, > > > > I'm trying to find all paths between two nodes when relations can be of > one > > of two types (A or B) without repeating the same node twice - so far > quite > > simple. > > the complication is that relations of type A have a property P and I want > > only paths where P has the same value all the way (but can have two > > different values in two different paths). > > I tried to have a variable that is reset every time the traverse "starts > > again from the beginning" but find it difficult to know when did this > > happen. position.length() helps when I only have relations of type A - it > > does not ignore relations of type B which can be on the path. > > iterating over the path at each position works but seems inefficient - > I'd > > like to hear ideas for a more efficient solution. > > > > Amos. > > _______________________________________________ > > Neo4j mailing list > > User@lists.neo4j.org > > https://lists.neo4j.org/mailman/listinfo/user > > > > > > -- > Mattias Persson, [matt...@neotechnology.com] > Hacker, Neo Technology > www.neotechnology.com > _______________________________________________ > Neo4j mailing list > User@lists.neo4j.org > https://lists.neo4j.org/mailman/listinfo/user > -- David Montag Neo Technology, www.neotechnology.com Cell: 650.556.4411 david.mon...@neotechnology.com _______________________________________________ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
