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| <pre><span class="source-line-no">001</span><span id="line-1">/*</span> |
| <span class="source-line-no">002</span><span id="line-2"> * Licensed to the Apache Software Foundation (ASF) under one</span> |
| <span class="source-line-no">003</span><span id="line-3"> * or more contributor license agreements. See the NOTICE file</span> |
| <span class="source-line-no">004</span><span id="line-4"> * distributed with this work for additional information</span> |
| <span class="source-line-no">005</span><span id="line-5"> * regarding copyright ownership. The ASF licenses this file</span> |
| <span class="source-line-no">006</span><span id="line-6"> * to you under the Apache License, Version 2.0 (the</span> |
| <span class="source-line-no">007</span><span id="line-7"> * "License"); you may not use this file except in compliance</span> |
| <span class="source-line-no">008</span><span id="line-8"> * with the License. You may obtain a copy of the License at</span> |
| <span class="source-line-no">009</span><span id="line-9"> *</span> |
| <span class="source-line-no">010</span><span id="line-10"> * http://www.apache.org/licenses/LICENSE-2.0</span> |
| <span class="source-line-no">011</span><span id="line-11"> *</span> |
| <span class="source-line-no">012</span><span id="line-12"> * Unless required by applicable law or agreed to in writing, software</span> |
| <span class="source-line-no">013</span><span id="line-13"> * distributed under the License is distributed on an "AS IS" BASIS,</span> |
| <span class="source-line-no">014</span><span id="line-14"> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span> |
| <span class="source-line-no">015</span><span id="line-15"> * See the License for the specific language governing permissions and</span> |
| <span class="source-line-no">016</span><span id="line-16"> * limitations under the License.</span> |
| <span class="source-line-no">017</span><span id="line-17"> */</span> |
| <span class="source-line-no">018</span><span id="line-18">package org.apache.hadoop.hbase.util;</span> |
| <span class="source-line-no">019</span><span id="line-19"></span> |
| <span class="source-line-no">020</span><span id="line-20">import java.util.ArrayList;</span> |
| <span class="source-line-no">021</span><span id="line-21">import java.util.Iterator;</span> |
| <span class="source-line-no">022</span><span id="line-22">import java.util.List;</span> |
| <span class="source-line-no">023</span><span id="line-23">import java.util.concurrent.ThreadLocalRandom;</span> |
| <span class="source-line-no">024</span><span id="line-24">import java.util.stream.Stream;</span> |
| <span class="source-line-no">025</span><span id="line-25">import org.apache.yetus.audience.InterfaceAudience;</span> |
| <span class="source-line-no">026</span><span id="line-26"></span> |
| <span class="source-line-no">027</span><span id="line-27">import org.apache.hbase.thirdparty.com.google.common.base.Preconditions;</span> |
| <span class="source-line-no">028</span><span id="line-28"></span> |
| <span class="source-line-no">029</span><span id="line-29">/**</span> |
| <span class="source-line-no">030</span><span id="line-30"> * The simple version of reservoir sampling implementation. It is enough for the usage in HBase.</span> |
| <span class="source-line-no">031</span><span id="line-31"> * <p/></span> |
| <span class="source-line-no">032</span><span id="line-32"> * See https://en.wikipedia.org/wiki/Reservoir_sampling.</span> |
| <span class="source-line-no">033</span><span id="line-33"> */</span> |
| <span class="source-line-no">034</span><span id="line-34">@InterfaceAudience.Private</span> |
| <span class="source-line-no">035</span><span id="line-35">public class ReservoirSample<T> {</span> |
| <span class="source-line-no">036</span><span id="line-36"></span> |
| <span class="source-line-no">037</span><span id="line-37"> private final List<T> r;</span> |
| <span class="source-line-no">038</span><span id="line-38"></span> |
| <span class="source-line-no">039</span><span id="line-39"> private final int k;</span> |
| <span class="source-line-no">040</span><span id="line-40"></span> |
| <span class="source-line-no">041</span><span id="line-41"> private int n;</span> |
| <span class="source-line-no">042</span><span id="line-42"></span> |
| <span class="source-line-no">043</span><span id="line-43"> public ReservoirSample(int k) {</span> |
| <span class="source-line-no">044</span><span id="line-44"> Preconditions.checkArgument(k > 0, "negative sampling number(%s) is not allowed", k);</span> |
| <span class="source-line-no">045</span><span id="line-45"> r = new ArrayList<>(k);</span> |
| <span class="source-line-no">046</span><span id="line-46"> this.k = k;</span> |
| <span class="source-line-no">047</span><span id="line-47"> }</span> |
| <span class="source-line-no">048</span><span id="line-48"></span> |
| <span class="source-line-no">049</span><span id="line-49"> public void add(T t) {</span> |
| <span class="source-line-no">050</span><span id="line-50"> if (n < k) {</span> |
| <span class="source-line-no">051</span><span id="line-51"> r.add(t);</span> |
| <span class="source-line-no">052</span><span id="line-52"> } else {</span> |
| <span class="source-line-no">053</span><span id="line-53"> int j = ThreadLocalRandom.current().nextInt(n + 1);</span> |
| <span class="source-line-no">054</span><span id="line-54"> if (j < k) {</span> |
| <span class="source-line-no">055</span><span id="line-55"> r.set(j, t);</span> |
| <span class="source-line-no">056</span><span id="line-56"> }</span> |
| <span class="source-line-no">057</span><span id="line-57"> }</span> |
| <span class="source-line-no">058</span><span id="line-58"> n++;</span> |
| <span class="source-line-no">059</span><span id="line-59"> }</span> |
| <span class="source-line-no">060</span><span id="line-60"></span> |
| <span class="source-line-no">061</span><span id="line-61"> public void add(Iterator<T> iter) {</span> |
| <span class="source-line-no">062</span><span id="line-62"> iter.forEachRemaining(this::add);</span> |
| <span class="source-line-no">063</span><span id="line-63"> }</span> |
| <span class="source-line-no">064</span><span id="line-64"></span> |
| <span class="source-line-no">065</span><span id="line-65"> public void add(Stream<T> s) {</span> |
| <span class="source-line-no">066</span><span id="line-66"> s.forEachOrdered(this::add);</span> |
| <span class="source-line-no">067</span><span id="line-67"> }</span> |
| <span class="source-line-no">068</span><span id="line-68"></span> |
| <span class="source-line-no">069</span><span id="line-69"> public List<T> getSamplingResult() {</span> |
| <span class="source-line-no">070</span><span id="line-70"> return r;</span> |
| <span class="source-line-no">071</span><span id="line-71"> }</span> |
| <span class="source-line-no">072</span><span id="line-72">}</span> |
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| </pre> |
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