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From tillrohrmann <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-1901] [core] Create sample operator for...
Date Fri, 31 Jul 2015 15:36:58 GMT
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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