Class DenseSparceTransform

JSAT/src/jsat/datatransform/DenseSparceTransform.java:16–81

Dense sparce transform alters the vectors that store the numerical values. Based on a threshold in (0, 1), vectors will be converted from dense to sparce, sparce to dense, or left alone. @author Edward Raff

 * @author Edward Raff
 */
public class DenseSparceTransform implements DataTransform
{

    private static final long serialVersionUID = -1177913691660616290L;
    private double factor;

    /**
     * Creates a new Dense Sparce Transform. The <tt>factor</tt> gives the maximal 
     * percentage of values that may be non zero for a vector to be sparce. Any 
     * vector meeting the requirement will be converted to a sparce vector, and 
     * others made dense. If the factor is greater than or equal to 1, then all 
     * vectors will be made sparce. If less than or equal to 0, then all will 
     * be made dense. 
     * 
     * @param factor the fraction of the vectors values that may be non zero to qualify as sparce
     */
    public DenseSparceTransform(double factor)
    {
        this.factor = factor;
    }

    @Override
    public void fit(DataSet data)
    {
        //no - op, nothing we need to learn
    }
    
    @Override
    public DataPoint transform(DataPoint dp)
    {
        Vec orig = dp.getNumericalValues();

        final int nnz = orig.nnz();
        if (nnz / (double) orig.length() < factor)///make sparse
        {
            if(orig.isSparse())//already sparse, just return
                return dp;
            //else, make sparse
            SparseVector sv = new SparseVector(orig.length(), nnz);//TODO create a constructor for this 
            for(int i  = 0; i < orig.length(); i++)
                if(orig.get(i) != 0)
                    sv.set(i, orig.get(i));

            return new DataPoint(sv, dp.getCategoricalValues(), dp.getCategoricalData(), dp.getWeight());
        }
        else//make dense
        {
            if(!orig.isSparse())//already dense, just return
                return dp;
            DenseVector dv = new DenseVector(orig.length());
            Iterator<IndexValue> iter = orig.getNonZeroIterator();
            while (iter.hasNext())
            {
                IndexValue indexValue = iter.next();
                dv.set(indexValue.getIndex(), indexValue.getValue());
            }
            return new DataPoint(dv, dp.getCategoricalValues(), dp.getCategoricalData(), dp.getWeight());
        }