Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.mahout.cf.taste.impl.model; import java.util.Arrays; import java.util.Iterator; import java.util.List; import com.google.common.base.Function; import com.google.common.collect.Iterators; import org.apache.mahout.cf.taste.model.Preference; import org.apache.mahout.cf.taste.model.PreferenceArray; import org.apache.mahout.common.iterator.CountingIterator; /** * <p> * Like {@link GenericUserPreferenceArray} but stores preferences for one item (all item IDs the same) rather * than one user. * </p> * * @see BooleanItemPreferenceArray * @see GenericUserPreferenceArray * @see GenericPreference */ public final class GenericItemPreferenceArray implements PreferenceArray { private static final int USER = 0; private static final int VALUE = 2; private static final int VALUE_REVERSED = 3; private final long[] ids; private long id; private final float[] values; public GenericItemPreferenceArray(int size) { this.ids = new long[size]; values = new float[size]; this.id = Long.MIN_VALUE; // as a sort of 'unspecified' value } public GenericItemPreferenceArray(List<? extends Preference> prefs) { this(prefs.size()); int size = prefs.size(); long itemID = Long.MIN_VALUE; for (int i = 0; i < size; i++) { Preference pref = prefs.get(i); ids[i] = pref.getUserID(); if (i == 0) { itemID = pref.getItemID(); } else { if (itemID != pref.getItemID()) { throw new IllegalArgumentException("Not all item IDs are the same"); } } values[i] = pref.getValue(); } id = itemID; } /** * This is a private copy constructor for clone(). */ private GenericItemPreferenceArray(long[] ids, long id, float[] values) { this.ids = ids; this.id = id; this.values = values; } @Override public int length() { return ids.length; } @Override public Preference get(int i) { return new PreferenceView(i); } @Override public void set(int i, Preference pref) { id = pref.getItemID(); ids[i] = pref.getUserID(); values[i] = pref.getValue(); } @Override public long getUserID(int i) { return ids[i]; } @Override public void setUserID(int i, long userID) { ids[i] = userID; } @Override public long getItemID(int i) { return id; } /** * {@inheritDoc} * * Note that this method will actually set the item ID for <em>all</em> preferences. */ @Override public void setItemID(int i, long itemID) { id = itemID; } /** * @return all user IDs */ @Override public long[] getIDs() { return ids; } @Override public float getValue(int i) { return values[i]; } @Override public void setValue(int i, float value) { values[i] = value; } @Override public void sortByUser() { lateralSort(USER); } @Override public void sortByItem() { } @Override public void sortByValue() { lateralSort(VALUE); } @Override public void sortByValueReversed() { lateralSort(VALUE_REVERSED); } @Override public boolean hasPrefWithUserID(long userID) { for (long id : ids) { if (userID == id) { return true; } } return false; } @Override public boolean hasPrefWithItemID(long itemID) { return id == itemID; } private void lateralSort(int type) { //Comb sort: http://en.wikipedia.org/wiki/Comb_sort int length = length(); int gap = length; boolean swapped = false; while (gap > 1 || swapped) { if (gap > 1) { gap /= 1.247330950103979; // = 1 / (1 - 1/e^phi) } swapped = false; int max = length - gap; for (int i = 0; i < max; i++) { int other = i + gap; if (isLess(other, i, type)) { swap(i, other); swapped = true; } } } } private boolean isLess(int i, int j, int type) { switch (type) { case USER: return ids[i] < ids[j]; case VALUE: return values[i] < values[j]; case VALUE_REVERSED: return values[i] > values[j]; default: throw new IllegalStateException(); } } private void swap(int i, int j) { long temp1 = ids[i]; float temp2 = values[i]; ids[i] = ids[j]; values[i] = values[j]; ids[j] = temp1; values[j] = temp2; } @Override public GenericItemPreferenceArray clone() { return new GenericItemPreferenceArray(ids.clone(), id, values.clone()); } @Override public int hashCode() { return (int) (id >> 32) ^ (int) id ^ Arrays.hashCode(ids) ^ Arrays.hashCode(values); } @Override public boolean equals(Object other) { if (!(other instanceof GenericItemPreferenceArray)) { return false; } GenericItemPreferenceArray otherArray = (GenericItemPreferenceArray) other; return id == otherArray.id && Arrays.equals(ids, otherArray.ids) && Arrays.equals(values, otherArray.values); } @Override public Iterator<Preference> iterator() { return Iterators.transform(new CountingIterator(length()), new Function<Integer, Preference>() { @Override public Preference apply(Integer from) { return new PreferenceView(from); } }); } @Override public String toString() { if (ids == null || ids.length == 0) { return "GenericItemPreferenceArray[{}]"; } StringBuilder result = new StringBuilder(20 * ids.length); result.append("GenericItemPreferenceArray[itemID:"); result.append(id); result.append(",{"); for (int i = 0; i < ids.length; i++) { if (i > 0) { result.append(','); } result.append(ids[i]); result.append('='); result.append(values[i]); } result.append("}]"); return result.toString(); } private final class PreferenceView implements Preference { private final int i; private PreferenceView(int i) { this.i = i; } @Override public long getUserID() { return GenericItemPreferenceArray.this.getUserID(i); } @Override public long getItemID() { return GenericItemPreferenceArray.this.getItemID(i); } @Override public float getValue() { return values[i]; } @Override public void setValue(float value) { values[i] = value; } } }