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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 2011 David Jurgens
 *
 * 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.util;

import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;


/** 
 * A utility class for mapping a set of objects to unique indices.  The indices
 * returned by this class will always being at {@code 0}.
 *
 * @see Counter
 */
public interface Indexer extends Iterable> {

    /**
     * Adds the item and creates an index for it, returning that index.
     */
    int index(T item);

    /**
     * Adds an index for each item in the collection if it did not already
     * exist, returning {@code true} if at least one new index was added.
     */
    boolean indexAll(Collection items);

    /**
     * Removes all of the item-index mappings.
     */
    void clear();

    /**
     * Returns {@code true} if the item has a corresponding index
     */
    boolean contains(T item);

    /**
     * Returns an unmodifiable view of the items currently mapped to indices
     */
    Set items();

    /**
     * Returns the index for the item or a negative value corresponding to the
     * index the object would have been assigned if it had been added.
     */
    int find(T item);
    
    /**
     * Returns the highest index to which any element is mapped.
     */
    int highestIndex();

    /**
     * Returns an iterator over all the objects and their corresponding indices.
     * The returned iterator does not support {@code remove}.
     */
    Iterator> iterator();

    /**
     * Returns the element to which this index is mapped or {@code null} if the
     * index has not been mapped
     */
    T lookup(int index);

    /**
     * Returns an unmodifiable view from each index to the object mapped to that
     * index.
     */
    Map mapping();
    
    /**
     * Returns the number of items that are mapped to indices.
     */
    int size();
}