| //// |
| 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 |
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| 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 |
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| //// |
| [[operating-on-dropped-elements]] |
| == Operating on Dropped Elements |
| |
| One common scenario that happens when dropping elements using a traversal is the desire to perform |
| some sort of operation on the elements being removed. This simplest is returning |
| the number of elements being dropped from the traversal, which is shown in the example below from the |
| "modern" graph. |
| |
| [gremlin-groovy,modern] |
| ---- |
| g.V().has('lang', 'java').sideEffect(drop()).count() |
| ---- |
| |
| While this may seem a bit counterintuitive, what is occurring in this recipe is that the `sideEffect()` |
| step is performing the `drop()` while each of the input traverser is still passed along to the remainder |
| of the traversal, which in this case is a `count()` operation. This pattern can be extended beyond a |
| simple count to perform a variety of more complex traversals based on the dropped traversal such as |
| removing child nodes in the case of a tree or setting properties on adjacent vertices. |
| |
| WARNING: Some graph implementations may not behave in the same manner as TinkerGraph when using |
| side effects, such as the `sideEffect(drop())`. While the specified pattern works for TinkerGraph, we |
| recommend that this pattern be tested on your chosen implementation to ensure that it functions in the |
| same manner. |
