org.apache.pig.impl.builtin
Class RandomSampleLoader

java.lang.Object
  org.apache.pig.LoadFunc
      org.apache.pig.impl.builtin.SampleLoader
          org.apache.pig.impl.builtin.RandomSampleLoader

public class RandomSampleLoader
extends SampleLoader

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.

Field Summary

protected int

nextSampleIdx

Fields inherited from class org.apache.pig.impl.builtin.SampleLoader

loader, numSamples

Constructor Summary

RandomSampleLoader(String funcSpec, String ns)
Construct with a class of loader to use.

Method Summary

Tuple	getNext() Allocate a buffer for numSamples elements, populate it with the first numSamples tuples, and continue scanning rest of the input.
void	prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader, PigSplit split) Initializes LoadFunc for reading data.

Methods inherited from class org.apache.pig.impl.builtin.SampleLoader

computeSamples, getInputFormat, getLoadCaster, getNumSamples, relativeToAbsolutePath, setLocation, setNumSamples, setUDFContextSignature, skipNext

Methods inherited from class org.apache.pig.LoadFunc

getAbsolutePath, getPathStrings, join

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

nextSampleIdx

protected int nextSampleIdx

Constructor Detail

RandomSampleLoader

public RandomSampleLoader(String funcSpec,
                          String ns)

Construct with a class of loader to use.

Parameters:

funcSpec - func spec of the loader to use.

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.

Method Detail

getNext

public Tuple getNext()
              throws IOException

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

Specified by:

getNext in class LoadFunc

Returns:

the next tuple to be processed or null if there are no more tuples to be processed.

Throws:

IOException - if there is an exception while retrieving the next tuple

prepareToRead

public void prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader,
                          PigSplit split)
                   throws IOException

Description copied from class: LoadFunc

Initializes LoadFunc for reading data. This will be called during execution before any calls to getNext. The RecordReader needs to be passed here because it has been instantiated for a particular InputSplit.

Overrides:

prepareToRead in class SampleLoader

Parameters:

reader - RecordReader to be used by this instance of the LoadFunc

split - The input PigSplit to process

Throws:

IOException - if there is an exception during initialization