Gremlin: Calculate division of based on two counts in one line of code - orientdb

Question

I have two counts, calculated as follows:
1)g.V().hasLabel('brand').where(__.inE('client_brand').count().is(gt(0))).count()
2)g.V().hasLabel('brand').count()
and I want to get one line of code that results in the first count divided by the second.

Answer 1

Here's one way to do it:
g.V().hasLabel('brand').
fold().as('a','b').
math('a/b').
by(unfold().where(inE('client_brand')).count())
by(unfold().count())
Note that I simplify the first traversal to just .where(inE('client_brand')).count() since you only care to count that there is at least one edge, there's no need to count them all and do a compare.
You could also union() like:
g.V().hasLabel('brand').
union(where(inE('client_brand')).count(),
count())
fold().as('a','b').
math('a/b').
by(limit(local,1))
by(tail(local))
While the first one was a bit easier to read/follow, I guess the second is nicer because it only stores a list of the two counts whereas, the first stores a list of all the "brand" vertices which would be more memory intensive I guess.
Yet another way, provided by Daniel Kuppitz, that uses groupCount() in an interesting way:
g.V().hasLabel('brand').
groupCount().
by(choose(inE('client_brand'),
constant('a'),
constant('b'))).
math('a/(a+b)')
The following solution that uses sack() step shows why we have math() step:
g.V().hasLabel('brand').
groupCount().
by(choose(inE('client_brand'),
constant('a'),
constant('b'))).
sack(assign).
by(coalesce(select('a'), constant(0))).
sack(mult).
by(constant(1.0)). /* we need a double */
sack(div).
by(select(values).sum(local)).
sack()
If you can use lambdas then:
g.V().hasLabel('brand').
union(where(inE('client_brand')).count(),
count())
fold().
map{ it.get()[0]/it.get()[1]}

Answer 2

This is what worked for me:
g.V().limit(1).project('client_brand_count','total_brands')
.by(g.V().hasLabel('brand')
.where(__.inE('client_brand').count().is(gt(0))).count())
.by(g.V().hasLabel('brand').count())
.map{it.get().values()[0] / it.get().values()[1]}
.project('brand_client_pct')