Cousera Recommender System专项课程 Assignment2

第一问

package org.lenskit.mooc.nonpers.Imp;/*calculate the highest average rating*/import org.lenskit.mooc.nonpers.Util.MapSortByValue;
import org.lenskit.mooc.nonpers.Util.Rating;
import java.io.File;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.util.*;public class HighestAvgRating {public static void main(String[] args) throws Exception {ArrayList userId = new ArrayList();ArrayList movieId = new ArrayList();ArrayList rating = new ArrayList();File file = new File("data/ratings.csv");List<String> lines = Files.readAllLines(file.toPath(),StandardCharsets.UTF_8);for (String line : lines) {String[] array = line.split(",");userId.add(array[0]);movieId.add(array[1]);rating.add(array[2]);}userId.remove(0);movieId.remove(0);rating.remove(0);int count = 1;Double avg = null;List<Rating> list = new ArrayList<Rating>();HashMap<Long, Double> mean = new HashMap<>();for (int i = 0; i < userId.size(); i++) {list.add(new Rating(Long.parseLong(movieId.get(i).toString()),Double.parseDouble(rating.get(i).toString())));}for (int i = 0; i < list.size(); i++) {count = 1;Long tmp = list.get(i).getMovieid();Double k = list.get(i).getRatings();for (int j = i + 1; j < list.size(); j++) {if (tmp.equals(list.get(j).getMovieid())) {count++;k += list.get(j).getRatings();list.remove(list.get(j));j--;}}avg = k / count;mean.put(list.get(i).getMovieid(), avg);}for (Long key : MapSortByValue.sortByValue(mean).keySet()) {System.out.print(key + "-" + MapSortByValue.sortByValue(mean).get(key) + "\n");}}
}

Utils：

package org.lenskit.mooc.nonpers.Util;import java.util.*;public class MapSortByValue {//对map集合进行降序排序public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {List<Map.Entry<K, V>> list = new LinkedList<Map.Entry<K, V>>(map.entrySet());Collections.sort(list, new Comparator<Map.Entry<K, V>>(){@Overridepublic int compare(Map.Entry<K, V> o1, Map.Entry<K, V> o2){int compare = (o1.getValue()).compareTo(o2.getValue());return -compare;}});Map<K, V> result = new LinkedHashMap<K, V>();for (Map.Entry<K, V> entry : list) {result.put(entry.getKey(), entry.getValue());}return result;}
}

package org.lenskit.mooc.nonpers.Util;public class Rating {private Long movieid;private Double ratings;public Rating(){}public Rating(Long movieid,Double ratings){this.movieid = movieid;this.ratings = ratings;}public Long getMovieid() {return movieid;}public void setMovieid(Long movieid) {this.movieid = movieid;}public Double getRatings() {return ratings;}public void setRatings(Double ratings) {this.ratings = ratings;}
}

最终部分输出：

第二问

package org.lenskit.mooc.nonpers.Imp;import org.lenskit.mooc.nonpers.Util.MapSortByValue;
import org.lenskit.mooc.nonpers.Util.Rating;import java.io.File;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;public class DampedMeanRating {//set damping factor =5private  static  final double DAMPINGFACTOR = 5.0;public static <Dobule> void main(String[] args) throws Exception {ArrayList userId = new ArrayList();ArrayList movieId = new ArrayList();ArrayList rating = new ArrayList();File file = new File("data/ratings.csv");List<String> lines = Files.readAllLines(file.toPath(),StandardCharsets.UTF_8);for (String line : lines) {String[] array = line.split(",");userId.add(array[0]);movieId.add(array[1]);rating.add(array[2]);}userId.remove(0);movieId.remove(0);rating.remove(0);int count = 0;Double sum = 0.0;List<Rating> list = new ArrayList<>();HashMap<Long, Double> mean = new HashMap<>();for (int i = 0; i < userId.size(); i++) {list.add(new Rating(Long.parseLong(movieId.get(i).toString()),Double.parseDouble(rating.get(i).toString())));}for (int i = 0; i < list.size(); i++) {count++;sum += Double.parseDouble(list.get(i).getRatings().toString());}//calculate global meanDouble global_avg = sum/count;DampedAvgRating(global_avg, DAMPINGFACTOR);}//calculate damped meanpublic static Map DampedAvgRating(Double global_avg, Double DAMPINGFACTOR) throws IOException {ArrayList userId = new ArrayList();ArrayList movieId = new ArrayList();ArrayList rating = new ArrayList();File file = new File("data/ratings.csv");List<String> lines = Files.readAllLines(file.toPath(),StandardCharsets.UTF_8);for (String line : lines) {String[] array = line.split(",");userId.add(array[0]);movieId.add(array[1]);rating.add(array[2]);}userId.remove(0);movieId.remove(0);rating.remove(0);int count = 1;Double avg = null;List<Rating> list = new ArrayList<Rating>();HashMap<Long, Double> mean = new HashMap<>();for (int i = 0; i < userId.size(); i++) {list.add(new Rating(Long.parseLong(movieId.get(i).toString()),Double.parseDouble(rating.get(i).toString())));}for (int i = 0; i < list.size(); i++) {count = 1;Long tmp = list.get(i).getMovieid();Double k = list.get(i).getRatings();for (int j = i + 1; j < list.size(); j++) {if (tmp.equals(list.get(j).getMovieid())) {count++;k += list.get(j).getRatings();list.remove(list.get(j));//remove一个元素时，要把遍历的指针减一j--;}}avg = (k+(DAMPINGFACTOR*global_avg)) / (count+DAMPINGFACTOR);mean.put(list.get(i).getMovieid(), avg);}for (Long key : MapSortByValue.sortByValue(mean).keySet()) {System.out.print(key + "-" + MapSortByValue.sortByValue(mean).get(key) + "\n");}return  mean;}}

部分output

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