Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/949#discussion_r35985116
--- Diff:
flink-core/src/main/java/org/apache/flink/api/common/operators/util/ReservoirSamplerWithReplacement.java
---
@@ -0,0 +1,122 @@
+/*
+ * 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.flink.api.common.operators.util;
+
+import com.google.common.base.Preconditions;
+import org.apache.commons.math3.distribution.PoissonDistribution;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * A simple in memory implementation of Reservoir Sampling with
replacement, and with only one pass through
+ * the input iteration whose size is unpredictable.
+ * This implementation refers to the algorithm described in
"Reservoir-based Random Sampling with Replacement
+ * from Data Stream".
+ *
+ * @param <T> the type of sample.
+ */
+public class ReservoirSamplerWithReplacement<T> extends RandomSampler<T> {
+ private final int numSamples;
+ private final Random random;
+ private PoissonDistribution poissonDistribution;
+ private List<Integer> positions;
+
+ /**
+ * Create a reservoir sampler with fixed sample size and default random
number generator.
+ *
+ * @param numSamples number of samples to retain in reservoir, must be
non-negative.
+ */
+ public ReservoirSamplerWithReplacement(int numSamples) {
+ this(numSamples, new Random());
+ }
+
+ /**
+ * Create a reservoir sampler with fixed sample size and random number
generator seed.
+ *
+ * @param numSamples number of samples to retain in reservoir, must be
non-negative.
+ * @param seed random number generator seed
+ */
+ public ReservoirSamplerWithReplacement(int numSamples, long seed) {
+ this(numSamples, new Random(seed));
+ }
+
+ /**
+ * Create a reservoir sampler with fixed sample size and random number
generator.
+ *
+ * @param numSamples number of samples to retain in reservoir, must be
non-negative.
--- End diff --
"@param" is missing
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