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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..
 

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 getOutputFormat()
Gets the format of the output instances.
 o input(Instance)
Input an instance for filtering.
 o inputFormat(Instances)
Deprecated.
 o isOutputFormatDefined()
Returns whether the output format is ready to be collected
 o main(String[])
Main method for testing this class.
 o numPendingOutput()
Returns the number of instances pending output
 o output()
Output an instance after filtering and remove from the output queue.
 o outputFormat()
Deprecated.
 o outputPeek()
Output an instance after filtering but do not remove from the output queue.
 o setInputFormat(Instances)
Sets the format of the input instances.
 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
Note: inputFormat() is deprecated. use setInputFormat(Instances) instead.

 o setInputFormat
 public boolean setInputFormat(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 clears the output format and output queue, and the new batch flag is set. Overriders should call super.setInputFormat(Instances)

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()
Note: outputFormat() is deprecated. use getOutputFormat() instead.

 o getOutputFormat
 public final Instances getOutputFormat()
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: NullPointerException
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: NullPointerException
if the input format has not been defined.
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: NullPointerException
if no input structure has been defined,
Throws: Exception
if there was a problem finishing the batch.
 o output
 public Instance output()
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: NullPointerException
if no output structure has been defined
 o outputPeek
 public Instance outputPeek()
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: NullPointerException
if no input structure has been defined
 o numPendingOutput
 public int numPendingOutput()
Returns the number of instances pending output

Returns:
the number of instances pending output
Throws: NullPointerException
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
 o main
 public static void main(String args[])
Main method for testing this class.

Parameters:
argv - should contain arguments to the filter: use -h for help

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