Github user dkuppitz commented on a diff in the pull request: https://github.com/apache/tinkerpop/pull/531#discussion_r95639012 --- Diff: docs/src/recipes/duplicate-edge.asciidoc --- @@ -0,0 +1,142 @@ +//// +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. +//// +[[duplicate-edge]] +Duplicate Edge Detection +------------------------ + +Whether part of a graph maintenance process or for some other analysis need, it is sometimes necessary to detect +if there is more than one edge between two vertices. The following examples will assume that an edge with the same +label and direction will be considered "duplicate". + +The "modern" graph does not have any duplicate edges that fit that definition, so the following example adds one +that is duplicative of the "created" edge between vertex "1" and "3". + +[gremlin-groovy,modern] +---- +g.V(1).as("a").V(3).addE("created").from("a").iterate() +g.V(1).outE("created") +---- + +One way to find the duplicate edges would be to do something like this: + +[gremlin-groovy,existing] +---- +g.V().outE(). + project("a","b"). <1> + by().by(inV().path().by().by(label)). + group(). <2> + by(select("b")). + by(select("a").fold()). + unfold(). <3> + select(values). <4> + where(count(local).is(gt(1))) +---- + +<1> The "a" and "b" from the `project` contain the edge and the path respectively. The path consists of a the outgoing +vertex, an edge, and the incoming vertex. The use of `by().by(label))` converts the edge to its label (recall that `by` +are applied in round-robin fashion), so the path will look something like: `[v[1],created,v[3]]`. +<2> Group by the path from "b" and construct a list of edges from "a". Any value in this `Map` that has a list of edges +greater than one means that there is more than one edge for that edge label between those two vertices (i.e. the `Map` +key). +<3> Unroll the key-value pairs in the `Map` of paths-edges. +<4> Only the values from the `Map` are needed and as mentioned earlier, those lists with more than one edge would +containa duplicate. + +This method find the duplicates, but does require more memory than other approaches. A slightly more complex approach +that uses less memory might look like this: + +[gremlin-groovy,existing] +---- +g.V().as("ov"). --- End diff -- Go home.........
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