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From cestella <...@git.apache.org>
Subject [GitHub] metron pull request #867: METRON-1350: Add reservoir sampling functions to S...
Date Wed, 13 Dec 2017 21:30:50 GMT
Github user cestella commented on a diff in the pull request:

    https://github.com/apache/metron/pull/867#discussion_r156790945
  
    --- Diff: metron-analytics/metron-statistics/src/main/java/org/apache/metron/statistics/sampling/UniformSampler.java
---
    @@ -0,0 +1,91 @@
    +/**
    + * 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.metron.statistics.sampling;
    +
    +import java.util.ArrayList;
    +import java.util.List;
    +import java.util.Random;
    +
    +public class UniformSampler implements Sampler {
    +  private List<Object> reservoir;
    +  private int seen = 0;
    +  private int size;
    +  private Random rng = new Random(0);
    +
    +  public UniformSampler() {
    +    this(DEFAULT_SIZE);
    +  }
    +
    +  public UniformSampler(int size) {
    +    this.size = size;
    +    reservoir = new ArrayList<>(size);
    +  }
    +
    +  @Override
    +  public Iterable<Object> get() {
    +    return reservoir;
    +  }
    +
    +  /**
    +   * Add an object to the reservoir
    +   * @param o
    +   */
    +  public void add(Object o) {
    +    if(o == null) {
    +      return;
    +    }
    +    if (reservoir.size() < size) {
    +      reservoir.add(o);
    +    } else {
    +      int rIndex = rng.nextInt(seen + 1);
    --- End diff --
    
    Just so I'm clear, up to the reservoir size, we add to the reservoir.  When we're past
the reservoir, we do a random replacement as per https://en.wikipedia.org/wiki/Reservoir_sampling


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