Apache Mahout: DataModel implementation which delegates to underlying DataModel, while allowing filtering of items

SelectiveItemDataModel.java

import org.apache.mahout.cf.taste.common.NoSuchItemException;
import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.impl.common.LongPrimitiveArrayIterator;
import org.apache.mahout.cf.taste.impl.common.LongPrimitiveIterator;
import org.apache.mahout.cf.taste.impl.model.GenericUserPreferenceArray;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.PreferenceArray;

import java.util.Collection;

public class SelectiveItemDataModel implements DataModel {
    private DataModel delegate;
    private FastIDSet retainedItemIDs;

    public SelectiveItemDataModel(DataModel delegate, FastIDSet retainedItemIDs) {
        this.delegate = delegate;
        this.retainedItemIDs = retainedItemIDs;
    }

    @Override
    public LongPrimitiveIterator getUserIDs() throws TasteException {
        return delegate.getUserIDs();
    }

    @Override
    public PreferenceArray getPreferencesFromUser(long userID) throws TasteException {
        PreferenceArray inPreferences = delegate.getPreferencesFromUser(userID);
        long[] inIDs = inPreferences.getIDs();

        int size = 0;
        long[] outIds = new long[inIDs.length];
        float[] outValues = new float[inIDs.length];
        for (int i = 0; i < inIDs.length; i++) {
            if (retainedItemIDs.contains(inIDs[i])) {
                outIds[size] = inPreferences.getItemID(i);
                outValues[size] = inPreferences.getValue(i);
                size++;
            }
        }

        PreferenceArray outPreferences = new GenericUserPreferenceArray(size);
        outPreferences.setUserID(0, inPreferences.getUserID(0));
        for (int i = 0; i < size; i++) {
            outPreferences.setItemID(i, outIds[i]);
            outPreferences.setValue(i, outValues[i]);
        }

        return outPreferences;
    }

    @Override
    public FastIDSet getItemIDsFromUser(long userID) throws TasteException {
        FastIDSet itemIDs = delegate.getItemIDsFromUser(userID).clone();
        itemIDs.retainAll(retainedItemIDs);
        return itemIDs;
    }

    @Override
    public LongPrimitiveIterator getItemIDs() throws TasteException {
        return new LongPrimitiveArrayIterator(retainedItemIDs.toArray());
    }

    @Override
    public PreferenceArray getPreferencesForItem(long itemID) throws TasteException {
        if (!retainedItemIDs.contains(itemID))
            throw new NoSuchItemException(itemID);

        return delegate.getPreferencesForItem(itemID);
    }

    @Override
    public Float getPreferenceValue(long userID, long itemID) throws TasteException {
        if (!retainedItemIDs.contains(itemID))
            return null;

        return delegate.getPreferenceValue(userID, itemID);
    }

    @Override
    public Long getPreferenceTime(long userID, long itemID) throws TasteException {
        if (!retainedItemIDs.contains(itemID))
            return null;

        return delegate.getPreferenceTime(userID, itemID);
    }

    @Override
    public int getNumItems() throws TasteException {
        return retainedItemIDs.size();
    }

    @Override
    public int getNumUsers() throws TasteException {
        return delegate.getNumUsers();
    }

    @Override
    public int getNumUsersWithPreferenceFor(long itemID) throws TasteException {
        if (!retainedItemIDs.contains(itemID))
            return 0;

        return delegate.getNumUsersWithPreferenceFor(itemID);
    }

    @Override
    public int getNumUsersWithPreferenceFor(long itemID1, long itemID2) throws TasteException {
        if (!retainedItemIDs.contains(itemID1) || !retainedItemIDs.contains(itemID2))
            return 0;

        return delegate.getNumUsersWithPreferenceFor(itemID1, itemID2);
    }

    @Override
    public void setPreference(long userID, long itemID, float value) throws TasteException {
        delegate.setPreference(userID, itemID, value);
    }

    @Override
    public void removePreference(long userID, long itemID) throws TasteException {
        delegate.removePreference(userID, itemID);
    }

    @Override
    public boolean hasPreferenceValues() {
        return delegate.hasPreferenceValues();
    }

    @Override
    public float getMaxPreference() {
        return delegate.getMaxPreference();
    }

    @Override
    public float getMinPreference() {
        return delegate.getMinPreference();
    }

    @Override
    public void refresh(Collection<Refreshable> alreadyRefreshed) {
        delegate.refresh(alreadyRefreshed);
    }
}