List of vertices that can be reached by a specified list of vertices

Question

Here's how my graph looks like.

g = TinkerGraph.open().traversal()
school1 = g.addV('school').property('id', '1').next()
school2 = g.addV('school').property('id', '2').next()
student1 = g.addV('student').property('id', '3').next() 
student2 = g.addV('student').property('id', '4').next()     
g.addE('students').from(school1).to(student1)
g.addE('students').from(school1).to(student2)
g.addE('students').from(school2).to(student1)

I want to find the out the students who are common to both the schools. To extend the logic, what'll happen if I want to write a generic infinite traversal logic for the same.

score 2 · Accepted Answer · answered Oct 26 '18 at 19:03

2

gremlin> g.V(school1).out('students').filter(__.in('students').is(school2)).valueMap(true)
==>[id:4,label:student,id:[3]]

Not sure what you mean by "write a generic infinite traversal logic for the same" though.

answered Oct 26 '18 at 19:03

Daniel Kuppitz

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This is what I meant by infinite generic traversal logic - g.V().has('tag', 'dev').hasLabel('school').has('id', '1').repeat(out().simplePath()).until(inE('students')).dedup().filter(__.repeat(in_().simplePath()).until(outE().outV().hasLabel('school').has('id', '2))) – Pranjal Oct 29 '18 at 12:54

score 0 · Answer 2 · answered Oct 26 '18 at 19:18

This can work

gremlin> schools = [ '1', '2' ]
==>1
==>2
gremlin> g.V().
......1>   has('school', 'id', within(schools)).
......2>   out('students').
......3>   groupCount().by('id').
......4>   unfold().
......5>   filter( select(values).is(eq(schools.size())) ).
......6>   select(keys)
==>3

Start with the list of schools. It's probably safe to assume that there would be fewer schools than students.
Traverse out() from the schools to the students. At this point, a student appear multiple times in the stream, once for each school they attended. I'm assuming that there would be only 1 edge between a specific school and a specific student.
Do a groupCount() to create a Map where for each entry, the key is the student id and the value is the number of schools for the student.
Use unfold() to operate on the entries in the Map.
The filter picks only the students connected to all school in the lists, i.e. the student's value count equals the number of schools in the list.
Finally select(keys) to return the student id as the result.

List of vertices that can be reached by a specified list of vertices

2 Answers2