Relatively new to gremlin and working with this query:
g.V().or(has('LOCATION', eq('IPLTINMYGT0')),
has('LOCATION', eq('IPLTINMYK01'))).
repeat(bothE().otherV()).emit().times(1).has('LOCATION',eq('FSHRIN01K00')).dedup().
path().by(valueMap('LOCATION')).dedup()
And this simple graph on gremlify:
https://gremlify.com/grrlq20ig57/1
When I vary the query from times(1) to times(2), the result that shows up in the times(1) query no longer shows up in the times(2) query. I'm guessing this can be read as 'at most 1 hop' or 'at most 2 hops' so I was expecting when I went to higher level hops the times(1) result would still be included. Any way to get the times(1) result to show up (in addition to the times(2) result) when issuing times(2) queries (or greater)? Does this behavior have anything to do with DFS vs BFS? Any help is appreciated. Thanks!
Your use of dedup() after has('LOCATION',eq('FSHRIN01K00')) is filtering away one of the vertices emitted when you do times(2). Therefore when you call path() it is only called once on the traverser that survives that filter. If you remove that dedup() you get both paths traversed.
Related
I want to retrieve the specific range of users(required for pagination) and want to retrieve the total count as well, I'm executing the below query which is retrieving the list of user vertices as expected but the total count is returned as BulkSet
Map<String, Object> result = gt.V().hasLabel("user").sideEffect(__.count().store("total"))
.order().by("name", Order.desc)
.range(0, 10).fold().as("list")
.select("list","total").next();
The output is as below
How do I get the correct count as a Long value instead of the BulkSet?
Paging with Gremlin is discussed here and references this blog post which provides additional information on the topic. Those resources should help you with your paging strategy.
You framed this question in terms of inquiring about BulkSet so it isn't quite a duplicate of the answer I referenced, so I will try to answer that much for you. BulkSet allows for an important traversal optimization in TinkerPop which helps reduce object propagation, thus reducing memory requirements for a particular query. It does this by holding the traverser object and its count where the count is the number of times that object has been added to the BulkSet. Calling size() or longSize() (where the latter returns a long and the former returns int) will return the summation of the counts and therefore the "correct" or actual count of the objects. A call to uniqueSize() will return actual size of the set which will be the unique objects within it.
If you want the size of the BulkSet you just need to count() it:
gt.V().hasLabel("user").sideEffect(__.count().store("total"))
.order().by("name", Order.desc)
.range(0, 10).fold().as("list")
.select("list","total")
.by().
.by(count(local))
That said, I don't think your traversal isn't really doing what you want . The sideEffect() is just counting the current traverser which will simply return "1" and then you store that "1" in the list "total". At least that's what I see with TinkerGraph:
gremlin> g.V().hasLabel("person").sideEffect(count().store("total")).range(0,1).fold().as('list').select('list','total').by().by(count(local))
==>[list:[v[1]],total:1]
gremlin> g.V().hasLabel("person").sideEffect(count().store("total")).range(0,10).fold().as('list').select('list','total').by().by(count(local))
==>[list:[v[1],v[2],v[4],v[6]],total:4]
Interesting that JanusGraph somehow gives you 114 rather than 10 for the "total". I'd not expect that. I'd consider avoiding reliance on that "feature" in the case it is a "bug" that is later "fixed". Instead, please consider the posts I'd provided and look at them for inspiration.
I'm working on a recommendation system that recommends other users. The first results should be the most "similar" users to the "searcher" user. Users respond to questions and the amount of questions responded in the same way is the amount of similarity.
The problem is that I don't know how to write the query
So in technical words I need to sort the users by the amount of edges that has specific property values, I tried with this query, I thought it should work but it doesn't work:
let query = g.V().hasLabel('user');
let search = __;
for (const question of searcher.questions) {
search = search.outE('response')
.has('questionId', question.questionId)
.has('answerId', question.answerId)
.aggregate('x')
.cap('x')
}
query = query.order().by(search.unfold().count(), order.asc);
Throws this gremlin internal error:
org.apache.tinkerpop.gremlin.process.traversal.step.util.BulkSet cannot be cast to org.apache.tinkerpop.gremlin.structure.Vertex
I also tried with multiple .by() for each question, but the result was not ordered by the amount of coincidence.
How can I write this query?
When you cap() an aggregate() it returns a BulkSet which is a Set that has counts for how many times each object exists in that Set. It behaves like a List when you iterate through it by unrolling each object the associated size of the count. So you get your error because the output of cap('x') is a BulkSet but because you are building search in a loop you are basically just calling outE('response') on that BulkSet and that's not valid syntax as has() expects a graph Element such as a Vertex as indicated by the error.
I think you would prefer something more like:
let query = g.V().hasLabel('user').
outE('response');
let search = [];
for (const question of searcher.questions) {
search.push(has('questionId', question.questionId).
has('answerId', question.answerId));
}
query = query.or(...search).
groupCount().
by(outV())
order(local).by(values, asc)
I may not have the javascript syntax exactly right (and I used spread syntax in my or() to just convey the idea quickly of what needs to happen) but basically the idea here is to filter edges that match your question criteria and then use groupCount() to count up those edges.
If you need to count users who have no connection then perhaps you could switch to project() - maybe like:
let query = g.V().hasLabel('user').
project('user','count').
by();
let search = [];
for (const question of searcher.questions) {
search.push(has('questionId', question.questionId).
has('answerId', question.answerId));
}
query = query.by(outE('response').or(...search).count()).
order().by('count', asc);
fwiw, I think you might consider a different schema for your data that might make this recommendation algorithm a bit more graph-like. A thought might be to make the question/answer a vertex (a "qa" label perhaps) and have edges go from the user vertex to the "qa" vertex. Then users directly link to the question/answers they gave. You can easily see by way of edges, a direct relationship, which users gave the same question/answer combination. That change allows the query to flow much more naturally when asking the question, "What users answered questions in the same way user 'A' did?"
g.V().has('person','name','A').
out('responds').
in('responds').
groupCount().
order(local).by(values)
With that change you can see that we can rid ourselves of all those has() filters because they are implicitly implied by the "responds" edges which encode them into the graph data itself.
Am I not using select() properly in my code? When I re-select("pair") for some reason, what it contained originally has been updated after performing some step. Shouldn't what was labeled using as() preserve what was contained?
g.V()
.hasLabel("Project")
.hasId("parentId","childId").as("pair")
.select("pair")
.hasId("parentId").as("parent")
.select("pair") // no longer what it was originally set to
I think this is expected. You (presumably) find two vertices with hasId("parentId","childId") and so the first select("pair") would of course show each vertex. But, then you filter again, hasId("parentId") and kill the traverser that contains the vertex with the id of "childId". It gets filtered away and therefore never triggers the second/last select("pair") step and would only therefore return the one vertex that has the id of "parentId".
I'm new to Gremlin and I can't figure out a simple query which will return all vertices of my graph which do not have any edges (ie: orphaned Vertex). Ideally I'd like those without any 'out' edge.
I've been reading and some questions/articles say I can interpret an out edge as a property, but that didn't work for me either. I've been looking at hasNot and filtering.
Any ideas?
Thanks
-John
You can simply do this:
g.V().not(outE())
Or if you want to find total orphans:
g.V().not(bothE())
Try this: g.V().as('a').where(out().count().is(0)).select('a')
But, depending on how many vertices you have, you can run into request rate too large exception (aka 429).
To avoid that you can do the query in ranges, if you know the id ranges of the vertices, or it can be some other property ranges. An id range based example is below:
g.V().has('id', gt(0)).has('id', lt(100)).as('a').where(out().count().is(0)).select('a')
g.V().has('id', gt(99)).has('id', lt(200)).as('a').where(out().count().is(0)).select('a')
....
and so on
I have designed a model in Neo4j in order to get paths from one station to another including platforms/legs involved. The model is depicted down here. Basically, I need a query to take me from NBW to RD. also shows the platforms and legs involved. I am struggling with the query. I get no result. Appreciate if someone helps.
Here is my cypher statement:
MATCH p = (a:Station)-[r:Goto|can_board|can_alight|has_platfrom*0..]->(c:Station)
WHERE (a.name='NBW')
AND c.name='RD'
RETURN p
Model:
As mentioned in the comments, in Cypher you can't use a directed variable-length relationship that uses differing directions for some of the relationships.
However, APOC Procedures just added the ability to expand based on sequences of relationships. You can give this a try:
MATCH (start:station), (end:station)
WHERE start.name='NBW' AND end.name='THT'
CALL apoc.path.expandConfig(start, {terminatorNodes:[end], limit:1,
relationshipFilter:'has_platform>, can_board>, goto>, can_alight>, <has_platform'}) YIELD path
RETURN path
I added a limit so that only the first (and shortest) path to your end station will be returned. Removing the limit isn't advisable, since this will continue to repeat the relationships in the expansion, going from station to station, until it finds all possible ways to get to your end station, which could hang your query.
EDIT
Regarding the new model changes, the reason the above will not work is because relationship sequences can't contain a variable-length sequence within them. You have 2 goto> relationships to traverse, but only one is specified in the sequence.
Here's an alternative that doesn't use sequences, just a whitelisting of allowed relationships. The spanningTree() procedure uses NODE_GLOBAL uniqueness so there will only be a single unique path to each node found (paths will not backtrack or revisit previously-visited nodes).
MATCH (start:station), (end:station)
WHERE start.name='NBW' AND end.name='RD'
CALL apoc.path.spanningTree(start, {terminatorNodes:[end], limit:1,
relationshipFilter:'has_platform>|can_board>|goto>|can_alight>|<has_platform'}) YIELD path
RETURN path
Your query is directed --> and not all of the relationships between your two stations run in the same direction. If you remove the relationship direction you will get a result.
Then once you have a result I think something like this could get you pointed in the right direction on extracting the particular details from the resulting path once you get that working.
Essentially I am assuming that everything you are interested in is in your path that is returned you just need to filter out the different pieces that are returned.
As #InverseFalcon points out this query should be limited in a larger graph or it could easily run away.
MATCH p = (a:Station)-[r:Goto|can_board|can_alight|has_platfrom*0..]-(c:Station)
WHERE (a.name='NBW')
AND c.name='THT'
RETURN filter( n in nodes(p) WHERE 'Platform' in labels(n)) AS Platforms