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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.