Adding the incoming edges of a vertex to a set property during a traversal

Question

What I would like to do is a depth first traversal, where on each step I add the incoming edge (actually the vertex) to a set. Ultimately I want each node in the step to have a list of incoming vertices that were traversed. Initially I was adding one to a simple property for each incoming edge :

g.V().has('Name', 'startnode').repeat(__.in()).emit().property('degree', union(values('degree'), constant(1)).sum())

I end up with a property degree which holds a count of incoming edges. I now want a set of incoming edges rather than just a count. something similar to :

g.V().has('Name', 'R1\\B').repeat(__.in()).emit().property(set, 'incoming', XXX)

It's that XXX. What do I need to set it to? i.e. the current incoming vertex in the traversal.

Do you want to add all edges that were traversed on the current path or only the last edge that led to the current vertex? — Daniel Kuppitz

Daniel Kuppitz Daniel Kuppitz · Accepted Answer · 2019-04-25T20:23:44

In order to get access to the edges, you need to traverse them explicitely.

gremlin> g = TinkerFactory.createModern().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
gremlin> g.V().hasLabel('software').
           repeat(__.inE().as('e').outV()).
             emit().
           property(set, 'incoming', select(last, 'e')).iterate()
gremlin> g.V().valueMap()
==>[incoming:[e[9][1-created->3],e[8][1-knows->4]],name:[marko],age:[29]]
==>[name:[vadas],age:[27]]
==>[name:[lop],lang:[java]]
==>[incoming:[e[11][4-created->3],e[10][4-created->5]],name:[josh],age:[32]]
==>[name:[ripple],lang:[java]]
==>[incoming:[e[12][6-created->3]],name:[peter],age:[35]]

I wouldn't recommend storing whole edges though; edge ids might be fine.

gremlin> g = TinkerFactory.createModern().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
gremlin> g.V().hasLabel('software').
           repeat(__.inE().as('e').outV()).
             emit().
           property(set, 'incoming', select(last, 'e').by(id)).iterate()
gremlin> g.V().valueMap()
==>[incoming:[9,8],name:[marko],age:[29]]
==>[name:[vadas],age:[27]]
==>[name:[lop],lang:[java]]
==>[incoming:[11,10],name:[josh],age:[32]]
==>[name:[ripple],lang:[java]]
==>[incoming:[12],name:[peter],age:[35]]

UPDATE

To collect the adjacent vertex ids, it would be:

gremlin> g.V().hasLabel('software').
           repeat(__.as('v').in()).
             emit().
           property(set, 'incoming', select(last, 'v').by(id)).iterate()
gremlin> g.V().valueMap()
==>[incoming:[3,4],name:[marko],age:[29]]
==>[name:[vadas],age:[27]]
==>[name:[lop],lang:[java]]
==>[incoming:[3,5],name:[josh],age:[32]]
==>[name:[ripple],lang:[java]]
==>[incoming:[3],name:[peter],age:[35]]

Adding the incoming edges of a vertex to a set property during a traversal

1 Answers