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MapReduce实现基于物品的协同过滤：
实现过程中需要执行多个mapreduce任务。
初始数据：
u1,i101,5.0 u1,i102,3.0 u1,i103,2.5 u2,i101,2.0 u2,i102,2.5 u2,i103,5.0 u2,i104,2.0 u3,i101,2.0 u3,i104,4.0 u3,i105,4.5 u3,i107,5.0 u4,i101,5.0 u4,i103,3.0 u4,i104,4.5 u4,i106,4.0 u5,i101,4.0 u5,i102,3.0 u5,i103,2.0 u5,i104,4.0 u5,i105,3.5 u5,i106,4.0
job1: 生成用户对物品喜爱度矩阵
数据：初始数据
map:
key=userid
value=item:grade
reduce:
key=userid
value=item:grade,item:grade
结果:
u1 i101:5.0,i102:3.0,i103:2.5 u2 i101:2.0,i102:2.5,i103:5.0,i104:2.0 u3 i107:5.0,i105:4.5,i104:4.0,i101:2.0 u4 i106:4.0,i103:3.0,i101:5.0,i104:4.5 u5 i104:4.0,i105:3.5,i106:4.0,i101:4.0,i102:3.0,i103:2.0
job2: 生成物品与物品的同现矩阵
数据：job1的结果数据
map:
例，将i101 ,i102 ,i103 循环组合
key=item:item
value=1
reduce:
key=item:item
value=n
结果:
i101:i104 4 i101:i105 2 i101:i106 2 i101:i107 1 i102:i101 3 i102:i102 3 i102:i103 3 i102:i104 2 i102:i105 1 i102:i106 1 i103:i101 4 i103:i102 3 i103:i103 4 i103:i104 3 i103:i105 1 i103:i106 2 i104:i101 4 i104:i102 2 i104:i103 3 i104:i104 4 i104:i105 2 i104:i106 2 i104:i107 1 i105:i101 2 i105:i102 1 i105:i103 1 i105:i104 2 i105:i105 2 i105:i106 1 i105:i107 1 i106:i101 2 i106:i102 1 i106:i103 2 i106:i104 2 i106:i105 1 i106:i106 2 i107:i101 1 i107:i104 1 i107:i105 1 i107:i107 1
job3：将同现矩阵和用户喜爱度矩阵进行相乘
数据：job1和job2的输出数据
map:
区分不同的数据进行处理，根据文件目录进行区分
FileSplit split = (FileSplit)context.getInputSplit();
dirName = split.getPath().getParent().getName();
job1的数据经过map处理：
i101 B:u1,5.0
i102 B:u1,3.0
i103 B:u1,2.5
job2的数据经过map处理：
i101 A:i101,5
key=item
value=B:u1,5.0或A:i101,5
reduce:
针对同一个item的数据，A的数据，分别和B的数据进行相乘
key=user
value=item,score
u2 i105,4.0
结果：
u2 i105,4.0 u1 i105,14.0 u4 i105,24.0 u3 i105,28.0 u5 i105,36.0 u2 i104,44.0 u1 i104,64.0 u4 i104,84.0 u3 i104,92.0 u5 i104,108.0 u2 i107,110.0 u1 i107,115.0 u4 i107,120.0 u3 i107,122.0 u5 i107,126.0 u2 i106,130.0 u1 i106,140.0 u4 i106,150.0 u3 i106,154.0 u5 i106,162.0 u2 i101,172.0 u1 i101,197.0 u4 i101,222.0 u3 i101,232.0 u5 i101,252.0 u2 i103,260.0 u1 i103,280.0 u4 i103,300.0 u3 i103,308.0 u5 i103,324.0 u2 i102,330.0 u1 i102,345.0 u4 i102,360.0 u3 i102,366.0 u5 i102,378.0 u2 i105,2.5 u1 i105,5.5 u5 i105,8.5 u2 i104,13.5 u1 i104,19.5 u5 i104,25.5 u2 i106,28.0 u1 i106,31.0 u5 i106,34.0 u2 i101,41.5 u1 i101,50.5 u5 i101,59.5 u2 i103,67.0 u1 i103,76.0 u5 i103,85.0 u2 i102,92.5 u1 i102,101.5 u5 i102,110.5 u2 i105,5.0 u1 i105,7.5 u4 i105,10.5 u5 i105,12.5 u2 i104,27.5 u1 i104,35.0 u4 i104,44.0 u5 i104,50.0 u2 i106,60.0 u1 i106,65.0 u4 i106,71.0 u5 i106,75.0 u2 i101,95.0 u1 i101,105.0 u4 i101,117.0 u5 i101,125.0 u2 i103,145.0 u1 i103,155.0 u4 i103,167.0 u5 i103,175.0 u2 i102,190.0 u1 i102,197.5 u4 i102,206.5 u5 i102,212.5 u2 i105,4.0 u4 i105,13.0 u3 i105,21.0 u5 i105,29.0 u2 i104,37.0 u4 i104,55.0 u3 i104,71.0 u5 i104,87.0 u2 i107,89.0 u4 i107,93.5 u3 i107,97.5 u5 i107,101.5 u2 i106,105.5 u4 i106,114.5 u3 i106,122.5 u5 i106,130.5 u2 i101,138.5 u4 i101,156.5 u3 i101,172.5 u5 i101,188.5 u2 i103,194.5 u4 i103,208.0 u3 i103,220.0 u5 i103,232.0 u2 i102,236.0 u4 i102,245.0 u3 i102,253.0 u5 i102,261.0 u3 i105,9.0 u5 i105,16.0 u3 i104,25.0 u5 i104,32.0 u3 i107,36.5 u5 i107,40.0 u3 i106,44.5 u5 i106,48.0 u3 i101,57.0 u5 i101,64.0 u3 i103,68.5 u5 i103,72.0 u3 i102,76.5 u5 i102,80.0 u4 i105,4.0 u5 i105,8.0 u4 i104,16.0 u5 i104,24.0 u4 i106,32.0 u5 i106,40.0 u4 i101,48.0 u5 i101,56.0 u4 i103,64.0 u5 i103,72.0 u4 i102,76.0 u5 i102,80.0 u3 i105,5.0 u3 i104,10.0 u3 i107,15.0 u3 i101,20.0
Job4: 矩阵乘法求和
map:
不做特殊处理
key:user
value:item,score
reduce:
将相同的user及item的score的值进行相加。
key:user
value:item,score
结果:
u1 i105:15.5 u1 i104:33.5 u1 i107:5.0 u1 i106:18.0 u1 i101:44.0 u1 i103:39.0 u1 i102:31.5 u2 i105:15.5 u2 i104:36.0 u2 i107:4.0 u2 i106:20.5 u2 i101:45.5 u2 i103:41.5 u2 i102:32.5 u3 i105:26.0 u3 i104:38.0 u3 i107:15.5 u3 i106:16.5 u3 i101:40.0 u3 i103:24.5 u3 i102:18.5 u4 i105:26.0 u4 i104:55.0 u4 i107:9.5 u4 i106:33.0 u4 i101:63.0 u4 i103:53.5 u4 i102:37.0 u5 i105:32.0 u5 i104:59.0 u5 i107:11.5 u5 i106:34.5 u5 i101:68.0 u5 i103:56.5 u5 i102:42.5
此结果为用户对各个物品的喜爱度。
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原文地址：http://www.cnblogs.com/one--way/p/5654232.html
