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Class weka.filters.Filter 

java.lang.Object
   |
   +----weka.filters.Filter
public abstract class Filter
extends Object
implements Serializable
An abstract class for instance filters: objects that take instances as input, carry out some transformation on the instance and then output the instance. The method implementations in this class assume that most of the work will be done in the methods overridden by subclasses.

A simple example of filter use. This example doesn't remove instances from the output queue until all instances have been input, so has higher memory consumption than an approach that uses output instances as they are made available:

  Filter filter = ..some type of filter..
  Instances instances = ..some instances..
  for (int i = 0; i < data.numInstances(); i++) {
    filter.input(data.instance(i));
  }
  filter.batchFinished();
  Instances newData = filter.outputFormat();
  Instance processed;
  while ((processed = filter.output()) != null) {
    newData.add(processed);
  }
  ..do something with newData..

Version:
$Revision: 1.7 $
Author:
Len Trigg (trigg@cs.waikato.ac.nz)

Constructor Index

o Filter()

Method Index

o batchFilterFile(Filter, String[])
Method for testing filters ability to process multiple batches.
o batchFinished()
Signify that this batch of input to the filter is finished.
o filterFile(Filter, String[])
Method for testing filters.
o input(Instance)
Input an instance for filtering.
o inputFormat(Instances)
Sets the format of the input instances.
o isOutputFormatDefined()
Returns whether the output format is ready to be collected
o numPendingOutput()
Returns the number of instances pending output
o output()
Output an instance after filtering and remove from the output queue.
o outputFormat()
Gets the format of the output instances.
o outputPeek()
Output an instance after filtering but do not remove from the output queue.
o useFilter(Instances, Filter)
Filters an entire set of instances through a filter and returns the new set.

Constructors

o Filter 
 public Filter()

Methods

o inputFormat 
 public boolean inputFormat(Instances instanceInfo) throws Exception
Sets the format of the input instances. If the filter is able to determine the output format before seeing any input instances, it does so here. This default implementation assumes the output format is determined when batchFinished() is called.

Parameters:
instanceInfo - an Instances object containing the input instance structure (any instances contained in the object are ignored - only the structure is required).
Returns:
true if the outputFormat may be collected immediately
Throws: Exception
if the inputFormat can't be set successfully
o outputFormat 
 public final Instances outputFormat() throws Exception
Gets the format of the output instances. This should only be called after input() or batchFinished() has returned true. The relation name of the output instances should be changed to reflect the action of the filter (eg: add the filter name and options).

Returns:
an Instances object containing the output instance structure only.
Throws: Exception
if no input structure has been defined (or the output format hasn't been determined yet)
o input 
 public boolean input(Instance instance) throws Exception
Input an instance for filtering. Ordinarily the instance is processed and made available for output immediately. Some filters require all instances be read before producing output, in which case output instances should be collected after calling batchFinished(). If the input marks the start of a new batch, the output queue is cleared. This default implementation assumes all instance conversion will occur when batchFinished() is called.

Parameters:
instance - the input instance
Returns:
true if the filtered instance may now be collected with output().
Throws: Exception
if the input instance was not of the correct format or if there was a problem with the filtering.
o batchFinished 
 public boolean batchFinished() throws Exception
Signify that this batch of input to the filter is finished. If the filter requires all instances prior to filtering, output() may now be called to retrieve the filtered instances. Any subsequent instances filtered should be filtered based on setting obtained from the first batch (unless the inputFormat has been re-assigned or new options have been set). This default implementation assumes all instance processing occurs during inputFormat() and input().

Returns:
true if there are instances pending output
Throws: Exception
if no input structure has been defined
o output 
 public Instance output() throws Exception
Output an instance after filtering and remove from the output queue.

Returns:
the instance that has most recently been filtered (or null if the queue is empty).
Throws: Exception
if no input structure has been defined
o outputPeek 
 public Instance outputPeek() throws Exception
Output an instance after filtering but do not remove from the output queue.

Returns:
the instance that has most recently been filtered (or null if the queue is empty).
Throws: Exception
if no input structure has been defined
o numPendingOutput 
 public int numPendingOutput() throws Exception
Returns the number of instances pending output

Returns:
the number of instances pending output
Throws: Exception
if no input structure has been defined
o isOutputFormatDefined 
 public boolean isOutputFormatDefined()
Returns whether the output format is ready to be collected

Returns:
true if the output format is set
o useFilter 
 public static Instances useFilter(Instances data,
                                   Filter filter) throws Exception
Filters an entire set of instances through a filter and returns the new set.

Parameters:
data - the data to be filtered
filter - the filter to be used
Returns:
the filtered set of data
Throws: Exception
if the filter can't be used successfully
o filterFile 
 public static void filterFile(Filter filter,
                               String options[]) throws Exception
Method for testing filters.

Parameters:
argv - should contain the following arguments:
-i input_file
-o output_file
-c class_index
or -h for help on options
Throws: Exception
if something goes wrong or the user requests help on command options
o batchFilterFile 
 public static void batchFilterFile(Filter filter,
                                    String options[]) throws Exception
Method for testing filters ability to process multiple batches.

Parameters:
argv - should contain the following arguments:
-i (first) input file
-o (first) output file
-r (second) input file
-s (second) output file
-c class_index
or -h for help on options
Throws: Exception
if something goes wrong or the user requests help on command options 
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