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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.text;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Map;


/**
 * An iterator over all tokens in a stream that replaces tokens if they have a
 * known replacement value.  This simplifies term substitutions, such as mapping
 * the both "banana" and "cat" to "bananacat".
 */
public class WordReplacementIterator implements Iterator {

    /**
     * The backing iterator that tokenizes the stream
     */
    private final Iterator baseIterator;

    /**
     * A mapping from original tokens to their subsituted value.
     */
    private final Map replacementMap;

    /**
     * The next token to return
     */
    private String next;

    public WordReplacementIterator(Iterator base,
                                   Map map) {
        baseIterator = base;
        replacementMap = map;
        next = null;
        advance();
    }

    /**
     * Advances to the next word in the token stream.
     */
    public void advance() {
        String s = null;
        if (baseIterator.hasNext())
            next = baseIterator.next();
        else
            next = null;
    }

    /**
     * Returns {@code true} if this iterator has additional tokens to return.
     */
    public boolean hasNext() {
        return next != null;
    }

    /**
     * Return the next token's replacement if such a replacement exists.  If no
     * replacement for the next token exists, the original token is returned.
     *
     * @return The next token stored in this iterator, replaced with a
     *          subsituted value if one exists.
     */
    public String next() {
        if (next == null)
            throw new NoSuchElementException();
        String replacement = replacementMap.get(next);
        replacement = (replacement == null) ? next : replacement;
        advance();
        return replacement;
    }

    /**
     * Throws an {@link UnsupportedOperationException} if called.
     */ 
    public void remove() {
        throw new UnsupportedOperationException("remove is not supported");
    }
}