Create a empty array inside a Gremlin traversal?

Question

This sounds silly but is there a way to create a empty array inside a Gremlin traversal?

For the query below:

g.V().has('person','name', 'marko').project('a', 'b').by().by()

I want to project b as an empty array. I have tried:

g.V().has('person','name', 'marko').project('a', 'b').by().by(constant("").fold())

But constant("").fold() is not actually empty constant("").fold().count() returns 1. This applies to constant(null).fold() as well.

score 5 · Answer 1 · answered Mar 22 '18 at 00:40

5

Is this what you are looking for

g.withSideEffect('x',[]).V().has('person','name','marko').project('a','b').by(select('x')).by('name')

==>[a:[],b:marko]

answered Mar 22 '18 at 00:40

Kelvin Lawrence

This works but just curious, is there a way to have the `withSideEffect` inside the `by`? – Glide Mar 23 '18 at 01:42

score 4 · Accepted Answer · answered Mar 23 '18 at 15:00

4

An empty array/collection would actually be a fold() of nothing. You'll get nothing if you filter everything, hence:

g.V().has('person','name','marko').
  project('a', 'b').
    by().
    by(__.not(identity()).fold())

answered Mar 23 '18 at 15:00

Daniel Kuppitz

2 Answers2