I'm sure there's already an SO question asking the same thing, but I have been unable to find it. Perhaps I just don't know the right words to express this question properly. Some context: I'm deciding if AWS Neptune is a good fit for an upcoming project. So, I apparently have access to a SPARQL engine and a Tinkerpop/Gremlin engine if that helps answer the question.
Let's say I have items in a graph database. Those items have a "property" called category. Is there away to get a max of 20 items from each distinct category?
I've scoured various SPARQL resources (e.g. the docs) and haven't found anything describing this sort of functionality, and I've never had to do this in my previous sparql encounters. Not to familiar TinkerPop and Gremlin, but my initial readings haven't touched on this either.
It's fairly straightforward with Gremlin. Using the air-routes graph which has a region property for each airport. The following query will return five airports or less for California and Texas (there are more than 5 in the graph for each state).
gremlin> g.V().has('airport','region',within('US-CA','US-TX')).
group().
by('region').
by(identity().limit(5).fold())
==>[US-TX:[v[3],v[8],v[11],v[33],v[38]],US-CA:[v[13],v[23],v[24],v[26],v[27]]]
EDITED: Added additional example where specific regions are not looked for.
gremlin> g.V().hasLabel('airport').
limit(50).
group().
by('region').
by(identity().limit(5).fold())
==>[US-FL:[v[9],v[15],v[16],v[19],v[25]],US-NV:[v[30]],US-HI:[v[37]],US-TX:[v[3],v[8],v[11],v[33],v[38]],US-WA:[v[22]],US-NY:[v[12],v[14],v[32],v[35]],US-NC:[v[21]],US-LA:[v[34]],GB-ENG:[v[49],v[50]],US-PA:[v[45]],US-DC:[v[7]],US-NM:[v[44]],US-AZ:[v[20],v[43]],US-TN:[v[4]],CA-BC:[v[48]],CA-ON:[v[47]],PR-U-A:[v[40]],US-MN:[v[17]],US-IL:[v[18]],US-AK:[v[2]],US-VA:[v[10]],US-CO:[v[31]],US-MD:[v[6]],US-IA:[v[36]],US-MA:[v[5]],US-CA:[v[13],v[23],v[24],v[26],v[27]],US-UT:[v[29]],US-OH:[v[41]],US-GA:[v[1]],US-MI:[v[46]]]