Github user dkuppitz commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/531#discussion_r95785972
--- Diff: docs/src/recipes/appendix.asciidoc ---
@@ -0,0 +1,226 @@
+////
+Licensed to the Apache Software Foundation (ASF) under one or more
+contributor license agreements. See the NOTICE file distributed with
+this work for additional information regarding copyright ownership.
+The ASF licenses this file to You under the Apache License, Version 2.0
+(the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+////
+Appendix
+========
+
+Many of the recipes are based on questions and answers provided on the
gremlin-users mailing list. This section
+contains a number of traversals from the mailing list 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('name','marko').as('marko').
+ addV('name','josh').as('josh').
+ addV('name','daniel').as('daniel').
+ addV('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()).
+ group().by(select('p').by('name')).
+ by(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(label, "student", "name", "Pete").as("s1").
+ addV(label, "student", "name", "Joe").as("s2").
+ addV(label, "class", "name", "Java's GC").as("c1").
+ addV(label, "class", "name", "FP Principles").as("c2").
+ addV(label, "class", "name", "Memory Management in C").as("c3").
+ addV(label, "class", "name", "Memory Management in C++").as("c4").
+ addV(label, "timeslot", "date", "11/25/2016", "fromTime", "10:00",
"toTime", "11:00").as("t1").
+ addV(label, "timeslot", "date", "11/25/2016", "fromTime", "11:00",
"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(valueMap("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._
--- End diff --
I think it's important to note that this is only for edge that point into
the same direction (`OUT` in the example). The solution for undirected edges is
pretty complicated (if we take into account that ids are not necessarily
sortable).
```
g.V().as("a").both().as("b").
groupCount().by(select("a","b")).unfold().
filter(select(values).is(gt(1))).
select(keys).not(__.as("x").select("done").unfold().as("y").
select("x","y").by(select("a")).by(select("b")).
where("x", eq("y"))).store("done")
```
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