Github user dkuppitz commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/531#discussion_r95638679
--- Diff: docs/src/recipes/connected-components.asciidoc ---
@@ -0,0 +1,82 @@
+////
+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.
+////
+[[connected-components]]
+Connected Components
+--------------------
+
+Gremlin can be used to find
link:https://en.wikipedia.org/wiki/Connected_component_(graph_theory)[connected
components]
+in a graph. Consider the following graph which has three connected
components:
+
+image:connected-components.png[width=600]
+
+[gremlin-groovy]
+----
+g.addV(id, "A").as("a").
+ addV(id, "B").as("b").
+ addV(id, "C").as("c").
+ addV(id, "D").as("d").
+ addV(id, "E").as("e").
+ addV(id, "F").
+ addE("link").from("a").to("b").
+ addE("link").from("b").to("c").
+ addE("link").from("d").to("e").iterate()
+----
+
+One way to detect the various subgraphs would be to do something like this:
+
+[gremlin-groovy,existing]
+----
+g.V().emit(cyclicPath().or().not(both())).repeat(both()).until(cyclicPath()).
<1>
+ aggregate("p").by(path()).cap("p").
<2>
+ unfold().limit(local, 1).dedup().
<3>
+ map(__.as("v").select("p").unfold().
<4>
+ filter(unfold().where(eq("v"))).
+ unfold().dedup().order().by(id).fold()
+ ).dedup()
<5>
+----
+
+<1> Iterate all vertices and repeatedly traverse over both incoming and
outgoing edges (TinkerPop doesn't support
+unidirectional graphs directly so it must be simulated by ignoring the
direction with `both`). Note the use of `emit`
+prior to `repeat` as this allows for return of a single length path.
+<2> Aggregate the emitted vertices to "p" and get their path information.
Calling `cap` at the end will push the
+aggregate path list into the traversal. It is within these paths that the
list of connected components will be
+identified. Obviously the paths list are duplicative in the sense that
they contains different paths travelled over
+the same vertices.
+<3> Unroll the elements in the path list with `unfold` and grab the first
vertex in each path and `dedup`.
+<4> Use the first vertex in each path to filter against the paths stored
in "p". When a path is found that has the
+vertex in it, dedup the vertices in the path, order it by the identifier.
Each path output from this `map` step
+represents a connected component.
+<5> The connected component list is duplicative given the nature of the
paths in "p", but now that the vertices within
+the paths are ordered, a final `dedup` will make the list of connective
components unique.
+
+NOTE: This is a nice example of where running smaller pieces of a large
Gremlin statement make it easier to see what
+is happening at each step. Consider running this example one line at a
time (or perhaps even in a step at a time) to
+see the output at each point.
+
+While the above approach returns results nicely, the traversal doesn't
appear to work with OLAP. A less efficient
+approach, but one more suited for OLAP execution looks quite similar but
does not use `dedup` as heavily (thus
+`GraphComputer` is forced to analyze far more paths):
+
+[gremlin-groovy,existing]
+----
+g.withComputer().V().emit(cyclicPath().or().not(both())).repeat(both()).until(cyclicPath()).
--- End diff --
I'm pretty sure that's not working in `tp32` (OLAP).
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