| /* |
| * 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.pig.impl.builtin; |
| |
| import java.io.IOException; |
| import java.util.Random; |
| |
| import org.apache.pig.data.Tuple; |
| import org.apache.hadoop.mapreduce.RecordReader; |
| import org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigSplit; |
| |
| /** |
| * A loader that samples the data. |
| * It randomly samples tuples from input. The number of tuples to be sampled |
| * has to be set before the first call to getNext(). |
| * see documentation of getNext() call. |
| */ |
| public class RandomSampleLoader extends SampleLoader { |
| |
| //array to store the sample tuples |
| Tuple [] samples = null; |
| //index into samples array to the next sample to be returned |
| protected int nextSampleIdx= 0; |
| |
| /** |
| * Construct with a class of loader to use. |
| * @param funcSpec func spec of the loader to use. |
| * @param ns Number of samples per map to collect. |
| * Arguments are passed as strings instead of actual types (FuncSpec, int) |
| * because FuncSpec only supports string arguments to |
| * UDF constructors. |
| */ |
| public RandomSampleLoader(String funcSpec, String ns) { |
| // instantiate the loader |
| super(funcSpec); |
| // set the number of samples |
| super.setNumSamples(Integer.valueOf(ns)); |
| } |
| |
| /** |
| * Allocate a buffer for numSamples elements, populate it with the |
| * first numSamples tuples, and continue scanning rest of the input. |
| * For every ith next() call, we generate a random number r s.t. 0<=r<i, |
| * and if r<numSamples we insert the new tuple into our buffer at position r. |
| * This gives us a random sample of the tuples in the partition. |
| */ |
| @Override |
| public Tuple getNext() throws IOException { |
| |
| if(samples != null){ |
| return getSample(); |
| } |
| //else collect samples |
| samples = new Tuple[numSamples]; |
| |
| // populate the samples array with first numSamples tuples |
| Tuple t = null; |
| for(int i=0; i<numSamples; i++){ |
| t = loader.getNext(); |
| if(t == null) |
| break; |
| samples[i] = t; |
| } |
| |
| // rowNum that starts from 1 |
| int rowNum = numSamples+1; |
| Random randGen = new Random(); |
| |
| if(t != null){ // did not exhaust all tuples |
| while(true){ |
| // collect samples until input is exhausted |
| int rand = randGen.nextInt(rowNum); |
| if(rand < numSamples){ |
| // pick this as sample |
| Tuple sampleTuple = loader.getNext(); |
| if(sampleTuple == null) |
| break; |
| samples[rand] = sampleTuple; |
| }else { |
| //skip tuple |
| if(!skipNext()) |
| break; |
| } |
| rowNum++; |
| } |
| } |
| |
| return getSample(); |
| } |
| |
| @Override |
| public void prepareToRead(RecordReader reader, PigSplit split) throws IOException { |
| super.prepareToRead(reader, split); |
| samples = null; |
| nextSampleIdx = 0; |
| } |
| |
| private Tuple getSample() { |
| if(nextSampleIdx < samples.length){ |
| return samples[nextSampleIdx++]; |
| } |
| else{ |
| return null; |
| } |
| } |
| |
| } |