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The S-Space Package is a Natural Language Processing library for distributional semantics representations. Distributional semantics representations model the meaning of words, phrases, and sentences as high dimensional vectors or probability distributions. The library includes common algorithms such as Latent Semantic Analysis, Random Indexing, and Latent Dirichlet Allocation. The S-Space package also includes software libraries for matrices, vectors, graphs, and numerous clustering algorithms.

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/*
 * Copyright 2010 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 edu.ucla.sspace.common.SemanticSpace;

import edu.ucla.sspace.matrix.AbstractMatrix;
import edu.ucla.sspace.matrix.Matrix;

import edu.ucla.sspace.vector.DoubleVector;
import edu.ucla.sspace.vector.Vectors;


/**
 * A {@link Matrix} implementation whose data is backed by a {@link
 * SemanticSpace}.  This class provides a bridge between numerical operations
 * that use the space's data and the results of the algorithm itself.
 */
public class SemanticSpaceMatrix extends AbstractMatrix {

    /**
     * The {@code SemanticSpace} whose data backs this matrix.
     */
    private final SemanticSpace sspace;    
    
    /**
     * A mapping from each row to the word in the {@code SemanticSpace} whose
     * vector corresponds to that row.
     */
    private final BiMap rowToWord;

    /**
     * The number of columns in the matrix.  This value is cached, rather than
     * computed, in order to check for later modifications to the underlying
     * {@code SemanticSpace}, which might render this class's index-word mapping
     * invalid.
     */
    private final int columns;

    /**
     * Creates a {@code Matrix} whose data is backed by the provided {@code
     * SemanticSpace}.  The rows of this matrix are not guaranteed to be mapped
     * to any specific ordering of the words in the {@code SemanticSpace}.
     * Further, once this matrix is created, the underlying semantic space
     * should not be modified in such a way as to add new rows or to change the
     * vector length.
     */
    public SemanticSpaceMatrix(SemanticSpace sspace) {
        this.sspace = sspace;
        rowToWord = new HashBiMap();
        columns = sspace.getVectorLength();

        for (String word : sspace.getWords())
            rowToWord.put(rowToWord.size(), word);
    }

    /**
     * Returns {@code true} if the underlying {@link SemanticSpace} was modified
     * after the initial row mapping performed in the constructor.
     */
    private boolean checkModifications() {
        return !(sspace.getWords().size() == rowToWord.size()
                 && columns == sspace.getVectorLength());
    }

    /**
     * Returns the row to which the provided term is mapped or {@link null} if
     * the term is not mapped to any row.
     */
    public Integer getRowIndex(String term) {
        return rowToWord.inverse().get(term);
    }

    /**
     * {@inheritDoc}
     */
    public DoubleVector getRowVector(int row) {
        if (row < 0 || row >= rowToWord.size())
            throw new IndexOutOfBoundsException("Row is out of bounds: " + row);
        return Vectors.asDouble(sspace.getVector(rowToWord.get(row)));
    }

    /**
     * {@inheritDoc}
     */
    public int columns() {
        return columns;
    }
    
    /**
     * {@inheritDoc}
     */
    public int rows() {
        return rowToWord.size();
    }

    /**
     * {@inheritDoc}
     */
    public void set(int row, int col, double val) {
        throw new UnsupportedOperationException(
            "Cannot modify SemanticSpace-backed matrix");
    }
    
    /**
     * {@inheritDoc}
     */
    public void setColumn(int column, DoubleVector values) {
        throw new UnsupportedOperationException(
            "Cannot modify SemanticSpace-backed matrix");
    }

    /**
     * {@inheritDoc}
     */
    public void setRow(int row, DoubleVector values) {
        throw new UnsupportedOperationException(
            "Cannot modify SemanticSpace-backed matrix");
    }
}