Simplest way to implement a Row Number in Gremlin

Question

I need to assign a unique, incrementing value to all Vertices in my graph. In SQL I'd use ROW_NUMBER. Is there a simple way in Gremlin? I'm hoping for something like this:

g.V().<some_step>()

Output:

1
2
3
...

Answer 1

I don't think I would try this on a large graph but for a modest sized graph you could try using the index step. Below is an example that uses the air-routes data set.

The index adds an incrementing index value to a list.

gremlin> g.V().limit(5).fold().index().unfold()
==>[v[0],0]
==>[v[1],1]
==>[v[2],2]
==>[v[3],3]
==>[v[4],4]

Using local scope you can access members of that list.

gremlin> g.V().limit(5).fold().index().unfold().limit(local,1)
==>v[0]
==>v[1]
==>v[2]
==>v[3]
==>v[4]

Using those techniques we could use the index value to add a new property to each airport. I just did the first 5 in this example.

gremlin> g.V().limit(5).
               fold().index().unfold().as('list').
               limit(local,1).
               property('index',select('list').tail(local))

==>v[0]
==>v[1]
==>v[2]
==>v[3]
==>v[4]

And check the results.

gremlin> g.V(1).valueMap()
==>[country:[US],code:[ATL],longest:[12390],city:[Atlanta],index:[1],lon:[-84.4281005859375],type:[airport],elev:[1026
],icao:[KATL],region:[US-GA],runways:[5],lat:[33.6366996765137],desc:[Hartsfield - Jackson Atlanta International Airpo
rt]]


gremlin> g.V(2).valueMap()
==>[country:[US],code:[ANC],longest:[12400],city:[Anchorage],index:[2],lon:[-149.996002197266],type:[airport],elev:[15
1],icao:[PANC],region:[US-AK],runways:[3],lat:[61.1744003295898],desc:[Anchorage Ted Stevens]]