经典算法题每日演练——第六题 协同推荐SlopeOne 算法

 1     /// <summary>
 2     /// 评分实体类
 3     /// </summary>
 4     public class Rating
 5     {
 6         /// <summary>
 7         /// 记录差值
 8         /// </summary>
 9         public float Value { get; set; }
10 
11         /// <summary>
12         /// 记录评分人数，方便公式中的 m 和 n 的值
13         /// </summary>
14         public int Freq { get; set; }
15 
16         /// <summary>
17         /// 记录打分用户的ID
18         /// </summary>
19         public HashSet<int> hash_user = new HashSet<int>();
20 
21         /// <summary>
22         /// 平均值
23         /// </summary>
24         public float AverageValue
25         {
26             get { return Value / Freq; }
27         }
28     }

 1     /// <summary>
 2     /// 产品类
 3     /// </summary>
 4     public class Product
 5     {
 6         public int ProductID { get; set; }
 7 
 8         public string ProductName { get; set; }
 9 
10         /// <summary>
11         /// 对产品的打分
12         /// </summary>
13         public float Score { get; set; }
14     }

  1 using System;
  2 using System.Collections.Generic;
  3 using System.Linq;
  4 using System.Text;
  5 
  6 namespace SupportCenter.Test
  7 {
  8     #region Slope One 算法
  9     /// <summary>
 10     /// Slope One 算法
 11     /// </summary>
 12     public class SlopeOne
 13     {
 14         /// <summary>
 15         /// 评分系统
 16         /// </summary>
 17         public static Dictionary<int, Product> dicRatingSystem = new Dictionary<int, Product>();
 18 
 19         public Dictionary<string, Rating> dic_Martix = new Dictionary<string, Rating>();
 20 
 21         public HashSet<int> hash_items = new HashSet<int>();
 22 
 23         #region 接收一个用户的打分记录
 24         /// <summary>
 25         /// 接收一个用户的打分记录
 26         /// </summary>
 27         /// <param name="userRatings"></param>
 28         public void AddUserRatings(IDictionary<int, List<Product>> userRatings)
 29         {
 30             foreach (var user1 in userRatings)
 31             {
 32                 //遍历所有的Item
 33                 foreach (var item1 in user1.Value)
 34                 {
 35                     //该产品的编号（具有唯一性）
 36                     int item1Id = item1.ProductID;
 37 
 38                     //该项目的评分
 39                     float item1Rating = item1.Score;
 40 
 41                     //将产品编号字存放在hash表中
 42                     hash_items.Add(item1.ProductID);
 43 
 44                     foreach (var user2 in userRatings)
 45                     {
 46                         //再次遍历item，用于计算俩俩 Item 之间的差值
 47                         foreach (var item2 in user2.Value)
 48                         {
 49                             //过滤掉同名的项目
 50                             if (item2.ProductID <= item1Id)
 51                                 continue;
 52 
 53                             //该产品的名字
 54                             int item2Id = item2.ProductID;
 55 
 56                             //该项目的评分
 57                             float item2Rating = item2.Score;
 58 
 59                             Rating ratingDiff;
 60 
 61                             //用表的形式构建矩阵
 62                             var key = Tools.GetKey(item1Id, item2Id);
 63 
 64                             //将俩俩 Item 的差值 存放到 Rating 中
 65                             if (dic_Martix.Keys.Contains(key))
 66                                 ratingDiff = dic_Martix[key];
 67                             else
 68                             {
 69                                 ratingDiff = new Rating();
 70                                 dic_Martix[key] = ratingDiff;
 71                             }
 72 
 73                             //方便以后以后userrating的编辑操作，（add)
 74                             if (!ratingDiff.hash_user.Contains(user1.Key))
 75                             {
 76                                 //value保存差值
 77                                 ratingDiff.Value += item1Rating - item2Rating;
 78 
 79                                 //说明计算过一次
 80                                 ratingDiff.Freq += 1;
 81                             }
 82 
 83                             //记录操作人的ID，方便以后再次添加评分
 84                             ratingDiff.hash_user.Add(user1.Key);
 85                         }
 86                     }
 87                 }
 88             }
 89         }
 90         #endregion
 91 
 92         #region 根据矩阵的值，预测出该Rating中的值
 93         /// <summary>
 94         /// 根据矩阵的值，预测出该Rating中的值
 95         /// </summary>
 96         /// <param name="userRatings"></param>
 97         /// <returns></returns>
 98         public IDictionary<int, float> Predict(List<Product> userRatings)
 99         {
100             Dictionary<int, float> predictions = new Dictionary<int, float>();
101 
102             var productIDs = userRatings.Select(i => i.ProductID).ToList();
103 
104             //循环遍历_Items中所有的Items
105             foreach (var itemId in this.hash_items)
106             {
107                 //过滤掉不需要计算的产品编号
108                 if (productIDs.Contains(itemId))
109                     continue;
110 
111                 Rating itemRating = new Rating();
112 
113                 // 内层遍历userRatings
114                 foreach (var userRating in userRatings)
115                 {
116                     if (userRating.ProductID == itemId)
117                         continue;
118 
119                     int inputItemId = userRating.ProductID;
120 
121                     //获取该key对应项目的两组AVG的值
122                     var key = Tools.GetKey(itemId, inputItemId);
123 
124                     if (dic_Martix.Keys.Contains(key))
125                     {
126                         Rating diff = dic_Martix[key];
127 
128                         //关键点：运用公式求解（这边为了节省空间，对角线两侧的值呈现奇函数的特性）
129                         itemRating.Value += diff.Freq * (userRating.Score + diff.AverageValue * ((itemId < inputItemId) ? 1 : -1));
130 
131                         //关键点：运用公式求解 累计每两组的人数
132                         itemRating.Freq += diff.Freq;
133                     }
134                 }
135 
136                 predictions.Add(itemId, itemRating.AverageValue);
137             }
138 
139             return predictions;
140         }
141         #endregion
142     }
143     #endregion
144 
145     #region 工具类
146     /// <summary>
147     /// 工具类
148     /// </summary>
149     public class Tools
150     {
151         public static string GetKey(int Item1Id, int Item2Id)
152         {
153             return (Item1Id < Item2Id) ? Item1Id + "->" + Item2Id : Item2Id + "->" + Item1Id;
154         }
155     }
156     #endregion
157 }

 1     public class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             SlopeOne test = new SlopeOne();
 6 
 7             Dictionary<int, List<Product>> userRating = new Dictionary<int, List<Product>>();
 8 
 9             //第一位用户
10             List<Product> list = new List<Product>()
11             {
12                 new Product(){ ProductID=1, ProductName="洗衣机",Score=5},
13                 new Product(){ ProductID=2, ProductName="电冰箱", Score=10},
14                 new Product(){ ProductID=3, ProductName="彩电", Score=10},
15                 new Product(){ ProductID=4, ProductName="空调", Score=5},
16             };
17 
18             userRating.Add(1000, list);
19 
20             test.AddUserRatings(userRating);
21 
22             userRating.Clear();
23             userRating.Add(1000, list);
24 
25             test.AddUserRatings(userRating);
26 
27             //第二位用户
28             list = new List<Product>()
29             {
30                 new Product(){ ProductID=1, ProductName="洗衣机",Score=4},
31                 new Product(){ ProductID=2, ProductName="电冰箱", Score=5},
32                 new Product(){ ProductID=3, ProductName="彩电", Score=4},
33                  new Product(){ ProductID=4, ProductName="空调", Score=10},
34             };
35 
36             userRating.Clear();
37             userRating.Add(2000, list);
38 
39             test.AddUserRatings(userRating);
40 
41             //第三位用户
42             list = new List<Product>()
43             {
44                 new Product(){ ProductID=1, ProductName="洗衣机", Score=4},
45                 new Product(){ ProductID=2, ProductName="电冰箱", Score=10},
46                 new Product(){ ProductID=4, ProductName="空调", Score=5},
47             };
48 
49             userRating.Clear();
50             userRating.Add(3000, list);
51 
52             test.AddUserRatings(userRating);
53 
54             //那么我们预测userID=3000这个人对 “彩电” 的打分会是多少？
55             var userID = userRating.Keys.FirstOrDefault();
56             var result = userRating[userID];
57 
58             var predictions = test.Predict(result);
59 
60             foreach (var rating in predictions)
61                 Console.WriteLine("ProductID= " + rating.Key + " Rating: " + rating.Value);
62         }
63     }