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https://issues.apache.org/jira/browse/TINKERPOP3-866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14943636#comment-14943636
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Marko A. Rodriguez commented on TINKERPOP3-866:
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I just tried to stub this idea. Its actually more involved then just keeping an
old version of {{GraphTraversal}} around. Here is where things go south...
Interfaces have new methods... Steps have new APIs... Strategies expect
certain APIs... ... thus, we need basically a full clone of all the steps,
strategies, etc. I don't think this will work.
At first, many of these are simply just cloning {{AddVertexStartStep}}.. but
then {{EventStrategy}} expects certain behaviors (interface methods) from the
step...... :/
> GroupStep and Traversal-Based Reductions
> ----------------------------------------
>
> Key: TINKERPOP3-866
> URL: https://issues.apache.org/jira/browse/TINKERPOP3-866
> Project: TinkerPop 3
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.0.1-incubating
> Reporter: Marko A. Rodriguez
> Assignee: Marko A. Rodriguez
> Labels: breaking
> Fix For: 3.1.0-incubating
>
>
> Right now {{GroupStep}} is defined as:
> {code}
> public final class GroupStep<S, K, V, R> extends ReducingBarrierStep<S,
> Map<K, R>> implements MapReducer, TraversalParent {
> private Traversal.Admin<S, K> keyTraversal = null;
> private Traversal.Admin<S, V> valueTraversal = null;
> private Traversal.Admin<Collection<V>, R> reduceTraversal = null;
> ...
> {code}
> Look at {{reduceTraversal}}. It takes a {{Collection<V>}} of "values" and
> reduces them to a "reduction" {{R}}. Why are we using {{Collection<V>}}, why
> is this not:
> {code}
> private Traversal.Admin<V, R> reduceTraversal = null;
> {code}
> Now, when a new {{K}} is created (and reduce is defined), we clone
> {{reduceTraversal}}. Thus, each key has a {{reduceTraversal}} (identical
> clones) that operate in a stream like fashion on {{V}} to yield {{R}}. This
> enables us to remove the {{Collection<V>}} (memory hog) and allows us to
> defined {{GroupCountStep}} in terms of {{GroupStep}} without (?limited?)
> computational cost. HOWEVER, this changes the API as people who did this:
> {code}
> g.V.group.by(label()).by(outE().count()).by(sum(local))
> {code}
> would now have to do this:
> {code}
> g.V.group.by(label()).by(outE().count()).by(sum())
> {code}
> Its very minor, given the speed up we would gain and the ability for us to
> now do "groupCount" efficiently on arbitrary values -- not just bulks (e.g.
> sacks).
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