SimpleStreamFilter (original) (raw)

This filter is a superclass for simple stream filters.

General notes:

• After the first call of batchFinished() the field m_FirstBatchDone is set to true.

Example:
The following code snippet uses the filter SomeFilter on a dataset that is loaded from filename.

import weka.core.; import weka.filters.; import java.io.*; ... SomeFilter filter = new SomeFilter(); // set necessary options for the filter Instances data = new Instances( new BufferedReader( new FileReader(filename))); Instances filteredData = Filter.useFilter(data, filter);

Implementation:
Only the following abstract methods need to be implemented:

• globalInfo()
• determineOutputFormat(Instances)
• process(Instance)

And the getCapabilities() method must return what kind of attributes and classes the filter can handle.

If more options are necessary, then the following methods need to be overriden:

• listOptions()
• setOptions(String[])
• getOptions()

To make the filter available from commandline one must add the following main method for correct execution ( must be replaced with the actual filter classname):

public static void main(String[] args) { runFilter(new (), args); }

Example implementation:

import weka.core.; import weka.core.Capabilities.; import weka.filters.*;

import java.util.Random;

public class SimpleStream extends SimpleStreamFilter {

public String globalInfo() { return "A simple stream filter that adds an attribute 'bla' at the end containing a random number."; }

public Capabilities getCapabilities() { Capabilities result = super.getCapabilities(); result.enableAllAttributes(); result.enableAllClasses(); result.enable(Capability.NO_CLASS); // filter doesn't need class to be set return result; }

protected Instances determineOutputFormat(Instances inputFormat) { Instances result = new Instances(inputFormat, 0); result.insertAttributeAt(new Attribute("bla"), result.numAttributes()); return result; }

protected Instance process(Instance inst) { double[] values = new double[inst.numAttributes() + 1]; for (int n = 0; n < inst.numAttributes(); n++) values[n] = inst.value(n); values[values.length - 1] = new Random().nextInt(); Instance result = new Instance(1, values); return result; }

public static void main(String[] args) { runFilter(new SimpleStream(), args); } }

Options:
Valid filter-specific options are:

-D
Turns on output of debugging information.