/**
* 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() {
selectionSort(USER);
}
@Override
public void sortByItem() { }
@Override
public void sortByValue() {
selectionSort(VALUE);
}
@Override
public void sortByValueReversed() {
selectionSort(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 selectionSort(int type) {
// I think this sort will prove to be too dumb, but, it's in place and OK for tiny, mostly sorted data
int max = length();
boolean sorted = true;
for (int i = 1; i < max; i++) {
if (isLess(i, i - 1, type)) {
sorted = false;
break;
}
}
if (sorted) {
return;
}
for (int i = 0; i < max; i++) {
int min = i;
for (int j = i + 1; j < max; j++) {
if (isLess(j, min, type)) {
min = j;
}
}
if (i != min) {
swap(i, min);
}
}
}
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;
}
}
}