Github user okram commented on a diff in the pull request:
https://github.com/apache/incubator-tinkerpop/pull/210#discussion_r52093310
--- Diff:
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/GraphFilter.java
---
@@ -0,0 +1,193 @@
+/*
+ * 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.
+ */
+
+package org.apache.tinkerpop.gremlin.process.computer;
+
+import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
+import
org.apache.tinkerpop.gremlin.process.traversal.step.filter.RangeGlobalStep;
+import org.apache.tinkerpop.gremlin.process.traversal.step.map.VertexStep;
+import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
+import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalUtil;
+import org.apache.tinkerpop.gremlin.structure.Direction;
+import org.apache.tinkerpop.gremlin.structure.Edge;
+import org.apache.tinkerpop.gremlin.structure.Vertex;
+
+import java.io.Serializable;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+
+/**
+ * GraphFilter is used by {@link GraphComputer} implementations to prune
the source graph data being loaded into the OLAP system.
+ * There are two types of filters: a {@link Vertex} filter and an {@link
Edge} filter.
+ * The vertex filter is a {@link Traversal} that can only check the id,
label, and properties of the vertex.
+ * The edge filter is a {@link Traversal} that starts at the vertex are
emits all legal incident edges.
+ * If no vertex filter is provided, then no vertices are filtered. If no
edge filter is provided, then no edges are filtered.
+ * The use of a GraphFilter can greatly reduce the amount of data
processed by the {@link GraphComputer}.
+ * For instance, for {@code g.V().count()}, there is no reason to load
edges, and thus, the edge filter can be {@code bothE().limit(0)}.
+ *
+ * @author Marko A. Rodriguez (http://markorodriguez.com)
+ */
+public final class GraphFilter implements Cloneable, Serializable {
+
+ public enum Legal {
+ YES, NO, MAYBE;
+
+ public boolean positive() {
+ return this != NO;
+ }
+
+ public boolean negative() {
+ return this == NO;
+ }
+ }
+
+ private Traversal.Admin<Vertex, Vertex> vertexFilter = null;
+ private Traversal.Admin<Vertex, Edge> edgeFilter = null;
+
+ private boolean allowNoEdges = false;
+ private Direction allowedEdgeDirection = Direction.BOTH;
+ private Set<String> allowedEdgeLabels = new HashSet<>();
+ //private boolean allowAllRemainingEdges = false;
+
+ public void setVertexFilter(final Traversal<Vertex, Vertex>
vertexFilter) {
+ if (!TraversalHelper.isLocalVertex(vertexFilter.asAdmin()))
+ throw
GraphComputer.Exceptions.vertexFilterAccessesIncidentEdges(vertexFilter);
+ this.vertexFilter = vertexFilter.asAdmin().clone();
+ }
+
+ public void setEdgeFilter(final Traversal<Vertex, Edge> edgeFilter) {
+ if (!TraversalHelper.isLocalStarGraph(edgeFilter.asAdmin()))
+ throw
GraphComputer.Exceptions.edgeFilterAccessesAdjacentVertices(edgeFilter);
+ this.edgeFilter = edgeFilter.asAdmin().clone();
+ if (this.edgeFilter.getEndStep() instanceof RangeGlobalStep && 0
== ((RangeGlobalStep) this.edgeFilter.getEndStep()).getHighRange())
+ this.allowNoEdges = true;
+ else if (this.edgeFilter.getStartStep() instanceof VertexStep) {
+ this.allowedEdgeLabels.clear();
+ this.allowedEdgeLabels.addAll(Arrays.asList(((VertexStep)
this.edgeFilter.getStartStep()).getEdgeLabels()));
+ this.allowedEdgeDirection = ((VertexStep)
this.edgeFilter.getStartStep()).getDirection();
+ //this.allowAllRemainingEdges = 1 ==
this.edgeFilter.getSteps().size();
+ }
+ }
+
+ /*public void compileFilters() {
--- End diff --
I was using `compileFilters()` at first, but then didn't need them. I left
it commented out just in case its something that might pop up in the future.
`GraphFilter` is very new and over this 3.2.0 push, I'm sure we will tweak here
and there. Just want people to know its around.
Regarding the `allowRemainingEdges`. Again, its something I didn't need,
but can easily add if we find a good use case.
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