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The S-Space Package is a collection of algorithms for building Semantic Spaces as well as a highly-scalable library for designing new distributional semantics algorithms. Distributional algorithms process text corpora and represent the semantic for words as high dimensional feature vectors. This package also includes matrices, vectors, and numerous clustering algorithms. These approaches are known by many names, such as word spaces, semantic spaces, or distributed semantics and rest upon the Distributional Hypothesis: words that appear in similar contexts have similar meanings.

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/*
 * Copyright 2009 Keith Stevens 
 *
 * This file is part of the S-Space package and is covered under the terms and
 * conditions therein.
 *
 * The S-Space package is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation and distributed hereunder to you.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS" AND NO REPRESENTATIONS OR WARRANTIES,
 * EXPRESS OR IMPLIED ARE MADE.  BY WAY OF EXAMPLE, BUT NOT LIMITATION, WE MAKE
 * NO REPRESENTATIONS OR WARRANTIES OF MERCHANT- ABILITY OR FITNESS FOR ANY
 * PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE OR DOCUMENTATION
 * WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER
 * RIGHTS.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see .
 */

package edu.ucla.sspace.index;

import edu.ucla.sspace.vector.Vector;

import java.util.Properties;


/**
 * A permutation function that provides windows of positions which are permuted
 * using the same function.  For instance, with a window size of 2, words 1 and
 * 2 positions away will be permuted once, words 3 and 4 positions away will be
 * permuted twice, etc.  This class supports the following properties:
 *
 * 
 *
 *  Property: {@value #WINDOW_LIMIT_PROPERTY }
 *       

 *      Default: {@value #DEFAULT_WINDOW_LIMIT}
 *
 * 
This variable sets the size of a permutation
 * window.
 *
 * 
 *
 * @author Keith Stevens
 */
public class WindowedPermutationFunction
        implements PermutationFunction {

    /**
     * The prefix for naming public properties.
     */
    public static final String PROPERTY_PREFIX = 
        "edu.ucla.sspace.index.WindowedPermutationFunction";

    /**
     * The property to set the window size.
     */
    public static final String WINDOW_LIMIT_PROPERTY =
        PROPERTY_PREFIX + ".window";

    /**
     * The default window limit to place on permutations.
     */
    public static final String DEFAULT_WINDOW_LIMIT = "1";

    /**
     * The backing permutation function to use.
     */
    private final PermutationFunction function;

    /**
     * The window size for permutations.
     */
    private final int windowSize;

    /**
     * Creates a {@code WindowedPermutationFunction} using the default system
     * {@code Properties}.
     */
    public WindowedPermutationFunction() {
        this(System.getProperties());
    }

    /**
     * Creates a {@code WindowedPermutationFunction} using a passed in {@code
     * Properties}.
     */
    public WindowedPermutationFunction(Properties props) {
        function = new DefaultPermutationFunction();
        windowSize = Integer.parseInt(props.getProperty(
                    WINDOW_LIMIT_PROPERTY, DEFAULT_WINDOW_LIMIT));
    }
    
    /**
     * {@inheritDoc}
     */
    public Vector permute(Vector v, int numPermutations) {
        return function.permute(v, numPermutations/windowSize);
    }
}