Using gremlin in scala

[hansl...@gmail.com]

Hi

I am new to gremlin using to detect cycle in a directed graph.

I believe following query in groovy does that, but I am unable to write it in scala

g.V().as("a").repeat(out().simplePath()).emit(loops().is(gt(1))).where(out().as("a")).path()

Appreciate any help.

Thanks.

--Hans

[Michael Pollmeier]

Please post some graph setup and expected results.

[HadoopMarc]

Hi Hans,

Check the class named "__" in the Java API. This class is necessary for anonymous traversals like the out().simplePath() traversal. In the groovy examples the __ is not visible. You could also look into gremlin-scala (authored by the other poster), I do not know how anonymous traversals are handled there.

Cheers,    Marc

Op dinsdag 19 september 2017 20:58:03 UTC+2 schreef hansl...@gmail.com:

[hansl...@gmail.com]

Thank you, Michael.

Here is the code snippet in scala script. I need to implement isDirectedGraphCyclic(TinkerGraph) to detect the cycle.

Thank you for the help.

--Hans

/*********************************************************/

{code}

import org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerGraph

def isDirectedGraphCyclic(graph: TinkerGraph): Boolean = {
  //Need to write the query similar to
  //g.V().as("a").repeat(out().simplePath()).emit(loops().is(gt(1))).where(out().as("a")).path()
  return true 
}

val graph = TinkerGraph.open
val g = graph.traversal
val vA = g.addV("a").next
val vB = g.addV("b").next
val vC = g.addV("c").next
val vD = g.addV("d").next

vA.addEdge("next", vB)
vA.addEdge("next", vD)
vC.addEdge("next", vA)
vC.addEdge("next", vD)

//Assert graph has no cycles
val resultNo = isDirectedGraphCyclic(graph)

//Add another edge and make sure it becomes cyclic
vB.addEdge("next", vC)
val resultYes = isDirectedGraphCyclic(graph)

{code}

/***********************************************/

[Michael Pollmeier]

Thanks for sharing, I also learned something from this :)
Here's how you can implement it with gremlin-scala

import gremlin.scala._
import org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerGraph

val graph = TinkerGraph.open.asScala

val vA = graph + "a"
val vB = graph + "b"
val vC = graph + "c"
val vD = graph + "d"
vA --- "next" --> vB
vA --- "next" --> vD
vC --- "next" --> vA
vC --- "next" --> vD

def isDirectedGraphCyclic: Boolean = {
  val paths = graph.V.as("a")
    .repeat(_.out.simplePath)
    .emit
    .where(_.out.as("a"))
    .toList

  paths.size == 0

}

//Assert graph has no cycles

assert(isDirectedGraphCyclic)

//Add another edge and make sure it becomes cyclic

vB --- "next" --> vC
assert(!isDirectedGraphCyclic)

[hansl...@gmail.com]

Thank you, Michael.

This looks good.

--Hans