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= Appendix

Many of the recipes are based on questions and answers provided on the
link:https://groups.google.com/forum/#!forum/gremlin-users[gremlin-users mailing list] or on
link:http://stackoverflow.com/questions/tagged/gremlin[StackOverflow]. This section contains those traversals from
those sources that do not easily fit any particular pattern (i.e. a recipe), but are nonetheless interesting and thus
remain good tools for learning Gremlin.

[[appendix-a]]
_For each person in a "follows" graph, determine the number of followers and list their names._

[gremlin-groovy]
----
g.addV().property('name','marko').as('marko').
  addV().property('name','josh').as('josh').
  addV().property('name','daniel').as('daniel').
  addV().property('name','matthias').as('matthias').
  addE('follows').from('josh').to('marko').
  addE('follows').from('matthias').to('josh').
  addE('follows').from('daniel').to('josh').
  addE('follows').from('daniel').to('marko').iterate()
g.V().as('p').
  map(__.in('follows').values('name').fold()).
  project('person','followers','numFollowers').
    by(select('p').by('name')).
    by().
    by(count(local))
----

It might also be alternatively written as:

[gremlin-groovy,existing]
----
g.V().group().
        by('name').
        by(project('numFollowers','followers').
             by(__.in('follows').count()).
             by(__.in('follows').values('name').fold())).next()
----

or even:

[gremlin-groovy,existing]
----
g.V().group().
        by('name').
        by(__.in('follows').values('name').fold().
            project('numFollowers','followers').
              by(count(local)).
              by()).next()
----

[[appendix-b]]
_In the "modern" graph, show each person, the software they worked on and the co-worker count for the software and
the names of those co-workers._

[gremlin-groovy,modern]
----
g.V().hasLabel("person").as("p").
  out("created").as("s").
  map(__.in("created").
    where(neq("p")).values("name").fold()).
  group().by(select("p").by("name")).
    by(group().by(select("s").by("name")).
    by(project("numCoworkers","coworkers").
         by(count(local)).by())).next()
----

[[appendix-c]]
_Assuming a graph of students, classes and times, detect students who have a conflicting schedule._

[gremlin-groovy]
----
g.addV("student").property("name", "Pete").as("s1").
  addV("student").property("name", "Joe").as("s2").
  addV("class").property("name", "Java's GC").as("c1").
  addV("class").property("name", "FP Principles").as("c2").
  addV("class").property("name", "Memory Management in C").as("c3").
  addV("class").property("name", "Memory Management in C++").as("c4").
  addV("timeslot").property("date", "11/25/2016").property("fromTime", "10:00").property("toTime", "11:00").as("t1").
  addV("timeslot").property("date", "11/25/2016").property("fromTime", "11:00").property("toTime", "12:00").as("t2").
  addE("attends").from("s1").to("c1").
  addE("attends").from("s1").to("c2").
  addE("attends").from("s1").to("c3").
  addE("attends").from("s1").to("c4").
  addE("attends").from("s2").to("c2").
  addE("attends").from("s2").to("c3").
  addE("allocated").from("c1").to("t1").
  addE("allocated").from("c1").to("t2").
  addE("allocated").from("c2").to("t1").
  addE("allocated").from("c3").to("t2").
  addE("allocated").from("c4").to("t2").iterate()
g.V().hasLabel("student").as("s").
  out("attends").as("c").
  out("allocated").as("t").
  select("s").
  out("attends").
  where(neq("c")).
  out("allocated").
  where(eq("t")).
  group().
    by(select("s").by("name")).
    by(group().by(select("t").by(elementMap("fromTime","toTime"))).
               by(select("c").dedup().values("name").fold())).next()
----

[[appendix-d]]
_In the "modern" graph, with a duplicate edge added, find the vertex pairs that have more than one edge between them._

[gremlin-groovy,modern]
----
g.V(1).as("a").V(3).addE("created").property("weight",0.4d).from("a").iterate()
g.V(1).outE("created")
g.V().as("a").
  out().as("b").
  groupCount().
    by(select("a","b")).
  unfold().
  filter(select(values).is(gt(1))).
  select(keys)
----

The following example assumes that the edges point in the `OUT` direction. Assuming undirected edges:

[gremlin-groovy,modern]
----
g.V().where(without("x")).as("a").
  outE().as("e").inV().as("b").
  filter(bothE().where(neq("e")).otherV().where(eq("a"))).store("x").
  select("a","b").dedup()
----

[[appendix-e]]
_In the "crew" graph, find vertices that match on a complete set of multi-properties._

[gremlin-groovy,theCrew]
----
places = ["centreville","dulles"];[]  // will not match as "purcellville" is missing
g.V().not(has("location", without(places))).
  where(values("location").is(within(places)).count().is(places.size())).
  elementMap()
places = ["centreville","dulles","purcellville"];[]
g.V().not(has("location", without(places))).
  where(values("location").is(within(places)).count().is(places.size())).
  elementMap()
----

[[appendix-f]]
_Methods for performing some basic mathematical operations in the "modern" graph._

[gremlin-groovy,modern]
----
g.V().values("age").sum() // sum all ages
g.V().values("age").fold(1, mult) // multiply all ages
g.withSack(0).V().values("age").sack(sum).sack(sum).by(constant(-1)).sack() // subtract 1
g.withSack(0).V().values("age").sack(sum).sack(sum).sack() // multiply by 2 (simple)
g.withSack(0).V().values("age").sack(sum).sack(mult).by(constant(2)).sack() // multiply by 2 (generally useful for multiplications by n)
----

_Method for doing a sum with division._

[gremlin-groovy]
----
g.addV().property(id, "a").as("a").
  addV().property(id, "b").as("b").
  addE("link").from("a").to("b").
  addE("link").from("b").to("a").
  addE("link").from("b").to("a").iterate()
g.withSack(0d).
   V("a").as("a").
   V("b").as("b").
     project("ab", "ba").
       by(inE("link").where(outV().as("a")).count()).
       by(outE("link").where(inV().as("a")).count()).
     sack(sum).by("ab").
     sack(div).by("ba").
     project("a", "b", "#(a,b)", "#(b,a)", "#(a,b) / #(b,a)").
       by(select("a")).
       by(select("b")).
       by("ab").
       by("ba").
       by(sack())
----

[[appendix-g]]
_Dropping a vertex, as well as the vertices related to that dropped vertex that are connected by a "knows" edge in the
"modern" graph_

[gremlin-groovy,modern]
----
g.V().has('name','marko').outE()
g.V().has('name','marko').sideEffect(out('knows').drop()).drop()
g.V().has('name','marko')
g.V(2,4,3)
----

[[appendix-h]]
_For the specified graph, find all neighbor vertices connected to "A" as filtered by datetime, those neighbor vertices
that don't have datetime vertices, and those neighbor vertices that have the label "dimon"._

[gremlin-groovy]
----
g.addV().property("name", "A").as("a").
  addV().property("name", "B").as("b").
  addV().property("name", "C").as("c").
  addV().property("name", "D").as("d").
  addV().property("name", "E").as("e").
  addV("dimon").property("name", "F").as("f").
  addV().property("name", "G").as("g").property("date", 20160818).
  addV().property("name", "H").as("h").property("date", 20160817).
  addE("rel").from("a").to("b").
  addE("rel").from("a").to("c").
  addE("rel").from("a").to("d").
  addE("rel").from("a").to("e").
  addE("rel").from("c").to("f").
  addE("occured_at").from("d").to("g").
  addE("occured_at").from("e").to("h").iterate()
// D and E have a valid datetime
g.V().has("name", "A").out("rel").
  union(where(out("occured_at").has("date", gte(20160817))),
        __.not(outE("occured_at")).coalesce(out().hasLabel("dimon"), identity())).
  elementMap()
// only E has a valid date
g.V().has("name", "A").out("rel").
  union(where(out("occured_at").has("date", lte(20160817))),
        __.not(outE("occured_at")).coalesce(out().hasLabel("dimon"), identity())).
  elementMap()
// only D has a valid date
g.V().has("name", "A").out("rel").
  union(where(out("occured_at").has("date", gt(20160817))),
        __.not(outE("occured_at")).coalesce(out().hasLabel("dimon"), identity())).
  elementMap()
// neither D nor E have a valid date
g.V().has("name", "A").out("rel").
  union(where(out("occured_at").has("date", lt(20160817))),
        __.not(outE("occured_at")).coalesce(out().hasLabel("dimon"), identity())).
  elementMap()
----

[[appendix-i]]
_Use element labels in a `select`._

[gremlin-groovy,modern]
----
g.V(1).as("a").
  both().
  map(group().by(label).by(unfold())).as("b").
  select("a","b").
  map(union(project("a").by(select("a")), select("b")).
  unfold().
  group().
    by(select(keys)).
    by(select(values)))
g.V().as("a").
  both().
  map(group().by(label).by(unfold())).as("b").
  select("a","b").
  group().
    by("a").
    by(select("b").
         group().
           by(select(keys)).
           by(select(values).fold())).
    unfold().
    map(union(select(keys).project("a").by(), select(values)).
    unfold().
    group().
      by(select(keys).unfold()).
      by(select(values).unfold().unfold().fold()))
----

[[appendix-j]]
_Sum edge weight with a coefficient._

[gremlin-groovy]
----
g.addV('person').property('name','alice').as('alice').
  addV('person').property('name','bobby').as('bobby').
  addV('person').property('name','cindy').as('cindy').
  addV('person').property('name','david').as('david').
  addV('person').property('name','eliza').as('eliza').
  addE('rates').from('alice').to('bobby').property('tag','ruby').property('value',9).
  addE('rates').from('bobby').to('cindy').property('tag','ruby').property('value',8).
  addE('rates').from('cindy').to('david').property('tag','ruby').property('value',7).
  addE('rates').from('david').to('eliza').property('tag','ruby').property('value',6).
  addE('rates').from('alice').to('eliza').property('tag','java').property('value',9).iterate()
 g.withSack(1.0).V().has("name","alice").
   repeat(outE("rates").has("tag","ruby").
          project("a","b","c").
            by(inV()).
            by(sack()).
            by("value").as("x").
          select("a").
          sack(mult).by(constant(0.5))).
      times(3).emit().
    select(all, "x").
    project("name","score").
      by(tail(local, 1).select("a").values("name")).
      by(unfold().
         sack(assign).by(select("b")).
         sack(mult).by(select("c")).
         sack().sum())
----