#1571 Add degree variance evolution operator

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+[#1559] add unit-tests
+
+# Please enter the commit message for your changes. Lines starting
+# with '#' will be ignored, and an empty message aborts the commit.
+#
+# Date:      Tue Aug 2 11:06:54 2022 +0200
+#
+# interactive rebase in progress; onto 5f1b5d5a004
+# Last commands done (3 commands done):
+#    reword dc25f24377f add help functions
+#    reword 22c9104636f add unit-tests
+# No commands remaining.
+# You are currently editing a commit while rebasing branch '#1559_min_max_avg_degree_evolution' on '5f1b5d5a004'.
+#
+# Changes to be committed:
+#	new file:   gradoop-temporal/src/test/java/org/gradoop/temporal/model/impl/operators/metric/AvgDegreeEvolutionTest.java
+#	new file:   gradoop-temporal/src/test/java/org/gradoop/temporal/model/impl/operators/metric/MaxDegreeEvolutionTest.java
+#	new file:   gradoop-temporal/src/test/java/org/gradoop/temporal/model/impl/operators/metric/MinDegreeEvolutionTest.java
+#

gradoop-temporal/src/main/java/org/gradoop/temporal/model/impl/operators/metric/DegreeVarianceEvolution.java

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+/*
+ * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
+ *
+ * Licensed 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.gradoop.temporal.model.impl.operators.metric;
+
+import org.apache.flink.api.java.DataSet;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.gradoop.flink.model.api.operators.UnaryBaseGraphToValueOperator;
+import org.gradoop.flink.model.impl.operators.sampling.functions.VertexDegree;
+import org.gradoop.temporal.model.api.TimeDimension;
+import org.gradoop.temporal.model.impl.TemporalGraph;
+import org.gradoop.temporal.model.impl.operators.metric.functions.TransformDeltaToAbsoluteDegreeTree;
+import org.gradoop.temporal.model.impl.operators.metric.functions.FlatMapVertexIdEdgeInterval;
+import org.gradoop.temporal.model.impl.operators.metric.functions.BuildTemporalDegreeTree;
+import org.gradoop.temporal.model.impl.operators.metric.functions.GroupDegreeTreesToVariance;
+
+import java.util.Objects;
+
+/**
+ * Operator that calculates the degree variance evolution of a temporal graph for the
+ * whole lifetime of the graph.
+ */
+public class DegreeVarianceEvolution implements UnaryBaseGraphToValueOperator<TemporalGraph, DataSet<Tuple2<Long, Double>>> {
+  /**
+   * The time dimension that will be considered.
+   */
+  private final TimeDimension dimension;
+
+  /**
+   * The degree type (IN, OUT, BOTH);
+   */
+  private final VertexDegree degreeType;
+
+  /**
+   * Creates an instance of this average degree evolution operator.
+   *
+   * @param degreeType the degree type to use (IN, OUT, BOTH).
+   * @param dimension  the time dimension to use (VALID_TIME, TRANSACTION_TIME).
+   */
+  public DegreeVarianceEvolution(VertexDegree degreeType, TimeDimension dimension) {
+    this.degreeType = Objects.requireNonNull(degreeType);
+    this.dimension = Objects.requireNonNull(dimension);
+  }
+
+  @Override
+  public DataSet<Tuple2<Long, Double>> execute(TemporalGraph graph) {
+    return graph.getEdges()
+    // 1) Extract vertex id(s) and corresponding time intervals
+    .flatMap(new FlatMapVertexIdEdgeInterval(dimension, degreeType))
+    // 2) Group them by the vertex id
+    .groupBy(0)
+    // 3) For each vertex id, build a degree tree data structure
+    .reduceGroup(new BuildTemporalDegreeTree())
+    // 4) Transform each tree to aggregated evolution
+    .map(new TransformDeltaToAbsoluteDegreeTree())
+    // 6) Merge trees together and calculate aggregation
+    .reduceGroup(new GroupDegreeTreesToVariance());
+  }
+}

gradoop-temporal/src/main/java/org/gradoop/temporal/model/impl/operators/metric/functions/GroupDegreeTreesToVariance.java

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+/*
+ * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
+ *
+ * Licensed 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.gradoop.temporal.model.impl.operators.metric.functions;
+
+import org.apache.flink.api.common.functions.GroupReduceFunction;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.util.Collector;
+import org.gradoop.common.model.impl.id.GradoopId;
+
+import java.util.TreeSet;
+import java.util.TreeMap;
+import java.util.SortedSet;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * A group reduce function that merges all Tuples (vId, degreeTree) to a dataset of tuples (time, aggDegree)
+ * that represents the aggregated degree value for the whole graph at the given time.
+ */
+public class GroupDegreeTreesToVariance
+implements GroupReduceFunction<Tuple2<GradoopId, TreeMap<Long, Integer>>, Tuple2<Long, Double>> {
+
+  /**
+   * Creates an instance of this group reduce function.
+   *
+   */
+  public GroupDegreeTreesToVariance() {
+
+  }
+
+  @Override
+  public void reduce(Iterable<Tuple2<GradoopId, TreeMap<Long, Integer>>> iterable,
+                     Collector<Tuple2<Long, Double>> collector) throws Exception {
+
+    // init necessary maps and set
+    HashMap<GradoopId, TreeMap<Long, Integer>> degreeTrees = new HashMap<>();
+    HashMap<GradoopId, Integer> vertexDegrees = new HashMap<>();
+    SortedSet<Long> timePoints = new TreeSet<>();
+
+    // convert the iterables to a hashmap and remember all possible timestamps
+    for (Tuple2<GradoopId, TreeMap<Long, Integer>> tuple : iterable) {
+      degreeTrees.put(tuple.f0, tuple.f1);
+      timePoints.addAll(tuple.f1.keySet());
+    }
+
+    int numberOfVertices = degreeTrees.size();
+
+    // Add default times
+    timePoints.add(Long.MIN_VALUE);
+
+    for (Long timePoint : timePoints) {
+      // skip last default time
+      if (Long.MAX_VALUE == timePoint) {
+        continue;
+      }
+      // Iterate over all vertices
+      for (Map.Entry<GradoopId, TreeMap<Long, Integer>> entry : degreeTrees.entrySet()) {
+        // Make sure the vertex is registered in the current vertexDegrees capture
+        if (!vertexDegrees.containsKey(entry.getKey())) {
+          vertexDegrees.put(entry.getKey(), 0);
+        }
+
+        // Check if timestamp is in tree, if not, take the lower key
+        if (entry.getValue().containsKey(timePoint)) {
+          vertexDegrees.put(entry.getKey(), entry.getValue().get(timePoint));
+        } else {
+          Long lowerKey = entry.getValue().lowerKey(timePoint);
+          if (lowerKey != null) {
+            vertexDegrees.put(entry.getKey(), entry.getValue().get(lowerKey));
+          }
+        }
+      }
+
+      Optional<Integer> opt = vertexDegrees.values().stream().reduce(Math::addExact);
+      Optional<Double> opt2 = Optional.empty();
+
+      double mean;
+
+      if (opt.isPresent()) {
+        mean = (double) opt.get() / (double) numberOfVertices;
+        opt2 = Optional.of(vertexDegrees.values().stream()
+        .mapToDouble(val -> (val - mean) * (val - mean)).sum());
+      }
+
+      opt2.ifPresent(val -> collector.collect(
+      new Tuple2<>(timePoint, val / (double) numberOfVertices)));
+    }
+  }
+}

gradoop-temporal/src/main/java/org/gradoop/temporal/model/impl/operators/metric/functions/TransformDeltaToAbsoluteDegreeTree.java

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+/*
+ * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
+ *
+ * Licensed 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.gradoop.temporal.model.impl.operators.metric.functions;
+
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.java.functions.FunctionAnnotation;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.gradoop.common.model.impl.id.GradoopId;
+
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * Replaces the degree tree, that just stores the degree changes for each time, with a degree tree that
+ * stores the actual degree of the vertex at that time.
+ */
+@FunctionAnnotation.ForwardedFields("f0")
+public class TransformDeltaToAbsoluteDegreeTree
+implements MapFunction<Tuple2<GradoopId, TreeMap<Long, Integer>>,
+Tuple2<GradoopId, TreeMap<Long, Integer>>> {
+
+  /**
+   * To reduce object instantiations.
+   */
+  private TreeMap<Long, Integer> absoluteDegreeTree;
+
+  @Override
+  public Tuple2<GradoopId, TreeMap<Long, Integer>> map(
+  Tuple2<GradoopId, TreeMap<Long, Integer>> vIdTreeMapTuple) throws Exception {
+    // init the degree and the temporal tree
+    int degree = 0;
+    absoluteDegreeTree = new TreeMap<>();
+
+    // aggregate the degrees
+    for (Map.Entry<Long, Integer> entry : vIdTreeMapTuple.f1.entrySet()) {
+      degree += entry.getValue();
+      absoluteDegreeTree.put(entry.getKey(), degree);
+    }
+    vIdTreeMapTuple.f1 = absoluteDegreeTree;
+    return vIdTreeMapTuple;
+  }
+}

gradoop-temporal/src/test/java/org/gradoop/temporal/model/impl/operators/metric/DegreeVarianceEvolutionTest.java

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+/*
+ * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
+ *
+ * Licensed 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.gradoop.temporal.model.impl.operators.metric;
+
+import org.apache.flink.api.common.typeinfo.TypeHint;
+import org.apache.flink.api.java.DataSet;
+import org.apache.flink.api.java.io.LocalCollectionOutputFormat;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.gradoop.common.model.impl.id.GradoopId;
+import org.gradoop.flink.model.impl.operators.sampling.functions.VertexDegree;
+import org.gradoop.temporal.model.api.TimeDimension;
+import org.gradoop.temporal.model.impl.TemporalGraph;
+import org.gradoop.temporal.util.TemporalGradoopTestBase;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+
+import static org.junit.Assert.assertTrue;
+
+@RunWith(Parameterized.class)
+public class DegreeVarianceEvolutionTest extends TemporalGradoopTestBase {
+  /**
+   * The expected in-degrees for each vertex label.
+   */
+  private static final List<Tuple2<Long, Double>> EXPECTED_IN_DEGREES = new ArrayList<>();
+  /**
+   * The expected out-degrees for each vertex label.
+   */
+  private static final List<Tuple2<Long, Double>> EXPECTED_OUT_DEGREES = new ArrayList<>();
+  /**
+   * The expected degrees for each vertex label.
+   */
+  private static final List<Tuple2<Long, Double>> EXPECTED_BOTH_DEGREES = new ArrayList<>();
+
+  static {
+    // IN DEGREES
+    EXPECTED_IN_DEGREES.add(new Tuple2<>(Long.MIN_VALUE, 0.0));
+    EXPECTED_IN_DEGREES.add(new Tuple2<>(0L, 0.1875));
+    EXPECTED_IN_DEGREES.add(new Tuple2<>(4L, 0.5));
+    EXPECTED_IN_DEGREES.add(new Tuple2<>(5L, 0.25));
+    EXPECTED_IN_DEGREES.add(new Tuple2<>(6L, 0.25));
+    EXPECTED_IN_DEGREES.add(new Tuple2<>(7L, 0.1875));
+
+    // OUT DEGREES
+    EXPECTED_OUT_DEGREES.add(new Tuple2<>(Long.MIN_VALUE, 0.0));
+    EXPECTED_OUT_DEGREES.add(new Tuple2<>(0L, 0.1875));
+    EXPECTED_OUT_DEGREES.add(new Tuple2<>(4L, 0.5));
+    EXPECTED_OUT_DEGREES.add(new Tuple2<>(5L, 0.25));
+    EXPECTED_OUT_DEGREES.add(new Tuple2<>(6L, 0.25));
+    EXPECTED_OUT_DEGREES.add(new Tuple2<>(7L, 0.1875));
+
+    // DEGREES
+    EXPECTED_BOTH_DEGREES.add(new Tuple2<>(Long.MIN_VALUE, 0.0));
+    EXPECTED_BOTH_DEGREES.add(new Tuple2<>(0L, 0.24000000000000005));
+    EXPECTED_BOTH_DEGREES.add(new Tuple2<>(4L, 0.64));
+    EXPECTED_BOTH_DEGREES.add(new Tuple2<>(5L, 0.16));
+    EXPECTED_BOTH_DEGREES.add(new Tuple2<>(6L, 0.56));
+    EXPECTED_BOTH_DEGREES.add(new Tuple2<>(7L, 0.24000000000000005));
+  }
+
+  /**
+   * The degree type to test.
+   */
+  @Parameterized.Parameter(0)
+  public VertexDegree degreeType;
+
+  /**
+   * The expected degree variance evolution for the given type.
+   */
+  @Parameterized.Parameter(1)
+  public List<Tuple2<Long, Double>> expectedDegrees;
+
+  /**
+   * The temporal graph to test the operator.
+   */
+  TemporalGraph testGraph;
+
+  /**
+   * The parameters to test the operator.
+   *
+   * @return three different vertex degree types with its corresponding expected degree evolution.
+   */
+  @Parameterized.Parameters(name = "Test degree type {0}.")
+  public static Iterable<Object[]> parameters() {
+    return Arrays.asList(
+    new Object[]{VertexDegree.IN, EXPECTED_IN_DEGREES},
+    new Object[]{VertexDegree.OUT, EXPECTED_OUT_DEGREES},
+    new Object[]{VertexDegree.BOTH, EXPECTED_BOTH_DEGREES});
+  }
+
+  /**
+   * Set up the test graph and create the id-label mapping.
+   *
+   * @throws Exception in case of an error
+   */
+  @Before
+  public void setUp() throws Exception {
+    testGraph = getTestGraphWithValues();
+    Collection<Tuple2<GradoopId, String>> idLabelCollection = new HashSet<>();
+    testGraph.getVertices().map(v -> new Tuple2<>(v.getId(), v.getLabel()))
+    .returns(new TypeHint<Tuple2<GradoopId, String>>() {
+    }).output(new LocalCollectionOutputFormat<>(idLabelCollection));
+    getExecutionEnvironment().execute();
+  }
+
+  /**
+   * Test the degree variance evolution operator.
+   *
+   * @throws Exception in case of an error.
+   */
+  @Test
+  public void testDegreeVariance() throws Exception {
+    Collection<Tuple2<Long, Double>> resultCollection = new ArrayList<>();
+
+    final DataSet<Tuple2<Long, Double>> resultDataSet = testGraph
+    .callForValue(new DegreeVarianceEvolution(degreeType, TimeDimension.VALID_TIME));
+
+    resultDataSet.output(new LocalCollectionOutputFormat<>(resultCollection));
+    getExecutionEnvironment().execute();
+
+    assertTrue(resultCollection.containsAll(expectedDegrees));
+    assertTrue(expectedDegrees.containsAll(resultCollection));
+  }
+}