Cassandra based Mahout user friend recommendations - cassandra

Question

I want to recommend a user , a list of users which the current user can add as friends.
I am using Cassandra and mahout. there is already a implementation of CassandraDataModel in mahout integration package. I want to use this class.
So my recommend-er class looks like follows
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 has 4 column familys
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";
i have a hard time understanding this class especially the column family's. is there any example where i can look for or if someone can explain will be great with a small example.?
javadoc says this
* <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>

Answer 1

All the following instructions about required column families by CassandraDataMdoel should be performed in cassandra-cli under the keyspace you created (recommender or other name).
1: Table users
userID is the row key, each itemID has a separate column name, and value is the preference:
CREATE COLUMN FAMILY users
WITH comparator = LongType
AND key_validation_class=LongType
AND default_validation_class=FloatType;
Insert values:
set users[0][0]='1.0';
set users[1][0]='3.0';
set users[2][2]='1.0';
2: Table items
itemID is the row key, each userID has a separate column name, and value is the preference:
CREATE COLUMN FAMILY items
WITH comparator = LongType
AND key_validation_class=LongType
AND default_validation_class=FloatType;
Insert Values:
set items[0][0]='1.0';
set items[0][1]='3.0';
set items[2][2]='1.0';
3: Table userIDs
This table just has one row, but many columns, i.e. each userID has a separate column:
CREATE COLUMN FAMILY userIDs
WITH comparator = LongType
AND key_validation_class=LongType;
Insert Values:
set userIDs[0][0]='';
set userIDs[0][1]='';
set userIDs[0][2]='';
4: Table itemIDs:
This table just has one row, but many columns, i.e. each itemID has a separate column:
CREATE COLUMN FAMILY itemIDs
WITH comparator = LongType
AND key_validation_class=LongType;
Insert Values:
set itemIDs[0][0]='';
set itemIDs[0][1]='';
set itemIDs[0][2]='';

Answer 2

Complementing the answer above, for Cassandra 2.0 the new syntax is the following, according that cli is deprecated.
Table users:
CREATE TABLE users (userID bigint, itemID bigint, value float, PRIMARY KEY (userID, itemID));
Table items:
CREATE TABLE items (itemID bigint, userID bigint, value float, PRIMARY KEY (itemID, userID));
Table userIDs:
CREATE TABLE userIDs (id bigint, userID bigint PRIMARY KEY(id, userID));
Table itemIDs:
CREATE TABLE itemIDs (id bigint, itemID bigint PRIMARY KEY(id, itemID));