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/**
* 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.eval;
import java.util.Arrays;
import java.util.List;
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.LongPrimitiveIterator;
import org.apache.mahout.cf.taste.impl.common.RunningAverage;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.PreferenceArray;
import org.apache.mahout.cf.taste.recommender.RecommendedItem;
import org.apache.mahout.cf.taste.recommender.Recommender;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Evaluate recommender by comparing order of all raw prefs with order in
* recommender's output for that user. Can also compare data models.
*/
public final class OrderBasedRecommenderEvaluator {
private static final Logger log = LoggerFactory.getLogger(OrderBasedRecommenderEvaluator.class);
private OrderBasedRecommenderEvaluator() {
}
public static void evaluate(Recommender recommender1,
Recommender recommender2,
int samples,
RunningAverage tracker,
String tag) throws TasteException {
printHeader();
LongPrimitiveIterator users = recommender1.getDataModel().getUserIDs();
while (users.hasNext()) {
long userID = users.nextLong();
List recs1 = recommender1.recommend(userID, samples);
List recs2 = recommender2.recommend(userID, samples);
FastIDSet commonSet = new FastIDSet();
long maxItemID = setBits(commonSet, recs1, samples);
FastIDSet otherSet = new FastIDSet();
maxItemID = Math.max(maxItemID, setBits(otherSet, recs2, samples));
int max = mask(commonSet, otherSet, maxItemID);
max = Math.min(max, samples);
if (max < 2) {
continue;
}
Long[] items1 = getCommonItems(commonSet, recs1, max);
Long[] items2 = getCommonItems(commonSet, recs2, max);
double variance = scoreCommonSubset(tag, userID, samples, max, items1, items2);
tracker.addDatum(variance);
}
}
public static void evaluate(Recommender recommender,
DataModel model,
int samples,
RunningAverage tracker,
String tag) throws TasteException {
printHeader();
LongPrimitiveIterator users = recommender.getDataModel().getUserIDs();
while (users.hasNext()) {
long userID = users.nextLong();
List recs1 = recommender.recommend(userID, model.getNumItems());
PreferenceArray prefs2 = model.getPreferencesFromUser(userID);
prefs2.sortByValueReversed();
FastIDSet commonSet = new FastIDSet();
long maxItemID = setBits(commonSet, recs1, samples);
FastIDSet otherSet = new FastIDSet();
maxItemID = Math.max(maxItemID, setBits(otherSet, prefs2, samples));
int max = mask(commonSet, otherSet, maxItemID);
max = Math.min(max, samples);
if (max < 2) {
continue;
}
Long[] items1 = getCommonItems(commonSet, recs1, max);
Long[] items2 = getCommonItems(commonSet, prefs2, max);
double variance = scoreCommonSubset(tag, userID, samples, max, items1, items2);
tracker.addDatum(variance);
}
}
public static void evaluate(DataModel model1,
DataModel model2,
int samples,
RunningAverage tracker,
String tag) throws TasteException {
printHeader();
LongPrimitiveIterator users = model1.getUserIDs();
while (users.hasNext()) {
long userID = users.nextLong();
PreferenceArray prefs1 = model1.getPreferencesFromUser(userID);
PreferenceArray prefs2 = model2.getPreferencesFromUser(userID);
prefs1.sortByValueReversed();
prefs2.sortByValueReversed();
FastIDSet commonSet = new FastIDSet();
long maxItemID = setBits(commonSet, prefs1, samples);
FastIDSet otherSet = new FastIDSet();
maxItemID = Math.max(maxItemID, setBits(otherSet, prefs2, samples));
int max = mask(commonSet, otherSet, maxItemID);
max = Math.min(max, samples);
if (max < 2) {
continue;
}
Long[] items1 = getCommonItems(commonSet, prefs1, max);
Long[] items2 = getCommonItems(commonSet, prefs2, max);
double variance = scoreCommonSubset(tag, userID, samples, max, items1, items2);
tracker.addDatum(variance);
}
}
/**
* This exists because FastIDSet has 'retainAll' as MASK, but there is
* no count of the number of items in the set. size() is supposed to do
* this but does not work.
*/
private static int mask(FastIDSet commonSet, FastIDSet otherSet, long maxItemID) {
int count = 0;
for (int i = 0; i <= maxItemID; i++) {
if (commonSet.contains(i)) {
if (otherSet.contains(i)) {
count++;
} else {
commonSet.remove(i);
}
}
}
return count;
}
private static Long[] getCommonItems(FastIDSet commonSet, Iterable recs, int max) {
Long[] commonItems = new Long[max];
int index = 0;
for (RecommendedItem rec : recs) {
Long item = rec.getItemID();
if (commonSet.contains(item)) {
commonItems[index++] = item;
}
if (index == max) {
break;
}
}
return commonItems;
}
private static Long[] getCommonItems(FastIDSet commonSet, PreferenceArray prefs1, int max) {
Long[] commonItems = new Long[max];
int index = 0;
for (int i = 0; i < prefs1.length(); i++) {
Long item = prefs1.getItemID(i);
if (commonSet.contains(item)) {
commonItems[index++] = item;
}
if (index == max) {
break;
}
}
return commonItems;
}
private static long setBits(FastIDSet modelSet, List items, int max) {
long maxItem = -1;
for (int i = 0; i < items.size() && i < max; i++) {
long itemID = items.get(i).getItemID();
modelSet.add(itemID);
if (itemID > maxItem) {
maxItem = itemID;
}
}
return maxItem;
}
private static long setBits(FastIDSet modelSet, PreferenceArray prefs, int max) {
long maxItem = -1;
for (int i = 0; i < prefs.length() && i < max; i++) {
long itemID = prefs.getItemID(i);
modelSet.add(itemID);
if (itemID > maxItem) {
maxItem = itemID;
}
}
return maxItem;
}
private static void printHeader() {
log.info("tag,user,samples,common,hamming,bubble,rank,normal,score");
}
/**
* Common Subset Scoring
*
* These measurements are given the set of results that are common to both
* recommendation lists. They only get ordered lists.
*
* These measures all return raw numbers do not correlate among the tests.
* The numbers are not corrected against the total number of samples or the
* number of common items.
* The one contract is that all measures are 0 for an exact match and an
* increasing positive number as differences increase.
*/
private static double scoreCommonSubset(String tag,
long userID,
int samples,
int subset,
Long[] itemsL,
Long[] itemsR) {
int[] vectorZ = new int[subset];
int[] vectorZabs = new int[subset];
long bubble = sort(itemsL, itemsR);
int hamming = slidingWindowHamming(itemsR, itemsL);
if (hamming > samples) {
throw new IllegalStateException();
}
getVectorZ(itemsR, itemsL, vectorZ, vectorZabs);
double normalW = normalWilcoxon(vectorZ, vectorZabs);
double meanRank = getMeanRank(vectorZabs);
// case statement for requested value
double variance = Math.sqrt(meanRank);
log.info("{},{},{},{},{},{},{},{},{}",
tag, userID, samples, subset, hamming, bubble, meanRank, normalW, variance);
return variance;
}
// simple sliding-window hamming distance: a[i or plus/minus 1] == b[i]
private static int slidingWindowHamming(Long[] itemsR, Long[] itemsL) {
int count = 0;
int samples = itemsR.length;
if (itemsR[0].equals(itemsL[0]) || itemsR[0].equals(itemsL[1])) {
count++;
}
for (int i = 1; i < samples - 1; i++) {
long itemID = itemsL[i];
if (itemsR[i] == itemID || itemsR[i - 1] == itemID || itemsR[i + 1] == itemID) {
count++;
}
}
if (itemsR[samples - 1].equals(itemsL[samples - 1]) || itemsR[samples - 1].equals(itemsL[samples - 2])) {
count++;
}
return count;
}
/**
* Normal-distribution probability value for matched sets of values.
* Based upon:
* http://comp9.psych.cornell.edu/Darlington/normscor.htm
*
* The Standard Wilcoxon is not used because it requires a lookup table.
*/
static double normalWilcoxon(int[] vectorZ, int[] vectorZabs) {
int nitems = vectorZ.length;
double[] ranks = new double[nitems];
double[] ranksAbs = new double[nitems];
wilcoxonRanks(vectorZ, vectorZabs, ranks, ranksAbs);
return Math.min(getMeanWplus(ranks), getMeanWminus(ranks));
}
/**
* vector Z is a list of distances between the correct value and the recommended value
* Z[i] = position i of correct itemID - position of correct itemID in recommendation list
* can be positive or negative
* the smaller the better - means recommendations are closer
* both are the same length, and both sample from the same set
*
* destructive to items arrays - allows N log N instead of N^2 order
*/
private static void getVectorZ(Long[] itemsR, Long[] itemsL, int[] vectorZ, int[] vectorZabs) {
int nitems = itemsR.length;
int bottom = 0;
int top = nitems - 1;
for (int i = 0; i < nitems; i++) {
long itemID = itemsR[i];
for (int j = bottom; j <= top; j++) {
if (itemsL[j] == null) {
continue;
}
long test = itemsL[j];
if (itemID == test) {
vectorZ[i] = i - j;
vectorZabs[i] = Math.abs(i - j);
if (j == bottom) {
bottom++;
} else if (j == top) {
top--;
} else {
itemsL[j] = null;
}
break;
}
}
}
}
/**
* Ranks are the position of the value from low to high, divided by the # of values.
* I had to walk through it a few times.
*/
private static void wilcoxonRanks(int[] vectorZ, int[] vectorZabs, double[] ranks, double[] ranksAbs) {
int nitems = vectorZ.length;
int[] sorted = vectorZabs.clone();
Arrays.sort(sorted);
int zeros = 0;
for (; zeros < nitems; zeros++) {
if (sorted[zeros] > 0) {
break;
}
}
for (int i = 0; i < nitems; i++) {
double rank = 0.0;
int count = 0;
int score = vectorZabs[i];
for (int j = 0; j < nitems; j++) {
if (score == sorted[j]) {
rank += j + 1 - zeros;
count++;
} else if (score < sorted[j]) {
break;
}
}
if (vectorZ[i] != 0) {
ranks[i] = (rank / count) * (vectorZ[i] < 0 ? -1 : 1); // better be at least 1
ranksAbs[i] = Math.abs(ranks[i]);
}
}
}
private static double getMeanRank(int[] ranks) {
int nitems = ranks.length;
double sum = 0.0;
for (int rank : ranks) {
sum += rank;
}
return sum / nitems;
}
private static double getMeanWplus(double[] ranks) {
int nitems = ranks.length;
double sum = 0.0;
for (double rank : ranks) {
if (rank > 0) {
sum += rank;
}
}
return sum / nitems;
}
private static double getMeanWminus(double[] ranks) {
int nitems = ranks.length;
double sum = 0.0;
for (double rank : ranks) {
if (rank < 0) {
sum -= rank;
}
}
return sum / nitems;
}
/**
* Do bubble sort and return number of swaps needed to match preference lists.
* Sort itemsR using itemsL as the reference order.
*/
static long sort(Long[] itemsL, Long[] itemsR) {
int length = itemsL.length;
if (length < 2) {
return 0;
}
if (length == 2) {
return itemsL[0].longValue() == itemsR[0].longValue() ? 0 : 1;
}
// 1) avoid changing originals; 2) primitive type is more efficient
long[] reference = new long[length];
long[] sortable = new long[length];
for (int i = 0; i < length; i++) {
reference[i] = itemsL[i];
sortable[i] = itemsR[i];
}
int sorted = 0;
long swaps = 0;
while (sorted < length - 1) {
// opportunistically trim back the top
while (length > 0 && reference[length - 1] == sortable[length - 1]) {
length--;
}
if (length == 0) {
break;
}
if (reference[sorted] == sortable[sorted]) {
sorted++;
} else {
for (int j = sorted; j < length - 1; j++) {
// do not swap anything already in place
int jump = 1;
if (reference[j] == sortable[j]) {
while (j + jump < length && reference[j + jump] == sortable[j + jump]) {
jump++;
}
}
if (j + jump < length && !(reference[j] == sortable[j] && reference[j + jump] == sortable[j + jump])) {
long tmp = sortable[j];
sortable[j] = sortable[j + 1];
sortable[j + 1] = tmp;
swaps++;
}
}
}
}
return swaps;
}
}
