基于 Cassandra 的 Mahout 用户好友推荐答案

【问题标题】：Cassandra based Mahout user friend recommendations基于 Cassandra 的 Mahout 用户好友推荐
【发布时间】：2014-02-26 20:17:35
【问题描述】：

我要推荐一个用户，当前用户可以加为好友的用户列表。

我正在使用 Cassandra 和 mahout。 mahout 集成包中已经有CassandraDataModel 的实现。我想用这个类。

所以我的推荐类如下所示

public class UserFriendsRecommender {

@Inject
private CassandraDataModel dataModel;

public List<RecommendedItem> recommend(Long userId, int number) throws TasteException{
    UserSimilarity userSimilarity = new PearsonCorrelationSimilarity(dataModel);
    // Optional:
    userSimilarity.setPreferenceInferrer(new AveragingPreferenceInferrer(dataModel));

    UserNeighborhood neighborhood =
              new NearestNUserNeighborhood(3, userSimilarity, dataModel);
    Recommender recommender = new GenericUserBasedRecommender(dataModel, neighborhood, userSimilarity); 
    Recommender cachingRecommender = new CachingRecommender(recommender);
    List<RecommendedItem> recommendations = cachingRecommender.recommend(userId, number);
    return recommendations;
}

}

CassandraDataModel 有 4 个列族

static final String USERS_CF = "users";
  static final String ITEMS_CF = "items";
  static final String USER_IDS_CF = "userIDs";
  static final String ITEM_IDS_CF = "itemIDs";

我很难理解这个类，尤其是列族的。有没有我可以寻找的例子，或者如果有人可以用一个小例子来解释会很好。

javadoc 这么说

* <p>
 * First, it uses a column family called "users". This is keyed by the user ID
 * as an 8-byte long. It contains a column for every preference the user
 * expresses. The column name is item ID, again as an 8-byte long, and value is
 * a floating point value represnted as an IEEE 32-bit floating poitn value.
 * </p>
 * 
 * <p>
 * It uses an analogous column family called "items" for the same data, but
 * keyed by item ID rather than user ID. In this column family, column names are
 * user IDs instead.
 * </p>
 * 
 * <p>
 * It uses a column family called "userIDs" as well, with an identical schema.
 * It has one row under key 0. It contains a column for every user ID in the
 * model. It has no values.
 * </p>
 * 
 * <p>
 * Finally it also uses an analogous column family "itemIDs" containing item
 * IDs.
 * </p>

【问题讨论】：

标签： cassandra mahout mahout-recommender

【解决方案1】：

以下关于 CassandraDataMdoel 所需列族的所有说明都应在您创建的键空间（推荐人或其他名称）下的 cassandra-cli 中执行。

1：表用户

userID是row key，每个itemID有一个单独的列名，value是preference：

CREATE COLUMN FAMILY users
WITH comparator = LongType
AND key_validation_class=LongType
AND default_validation_class=FloatType;

插入值：

set users[0][0]='1.0';
set users[1][0]='3.0';
set users[2][2]='1.0';

2：表格项

itemID为row key，每个userID有一个单独的column name，value为preference：

CREATE COLUMN FAMILY items
WITH comparator = LongType
AND key_validation_class=LongType
AND default_validation_class=FloatType;

插入值：

set items[0][0]='1.0';
set items[0][1]='3.0';
set items[2][2]='1.0';

3：表用户ID

这个表只有一行，但有很多列，即每个用户ID都有一个单独的列：

CREATE COLUMN FAMILY userIDs
WITH comparator = LongType
AND key_validation_class=LongType;

插入值：

set userIDs[0][0]='';
set userIDs[0][1]='';
set userIDs[0][2]='';

4：表项ID：

这个表只有一行，但有很多列，即每个 itemID 都有一个单独的列：

CREATE COLUMN FAMILY itemIDs
WITH comparator = LongType
AND key_validation_class=LongType;

插入值：

set itemIDs[0][0]='';
set itemIDs[0][1]='';
set itemIDs[0][2]='';

【讨论】：

【解决方案2】：

作为对上述答案的补充，对于 Cassandra 2.0，新语法如下，根据已弃用的 cli。

表用户：

CREATE TABLE users (userID bigint, itemID bigint, value float, PRIMARY KEY (userID, itemID));

表格项：

CREATE TABLE items (itemID bigint, userID bigint, value float, PRIMARY KEY (itemID, userID));

表用户 ID：

CREATE TABLE userIDs (id bigint, userID bigint PRIMARY KEY(id, userID));

表项 ID：

CREATE TABLE itemIDs (id bigint, itemID bigint PRIMARY KEY(id, itemID));

【讨论】：