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1. protected void reduce(VarIntWritable index,  
2.                         Iterable<VarLongWritable> possibleItemIDs,  
3.                         Context context) throws IOException, InterruptedException {  
4.     long minimumItemID = Long.MAX_VALUE;//获取Long类型最大值
5.     for (VarLongWritable varLongWritable : possibleItemIDs) {  //遍历possibleItemIDs
6.       long itemID = varLongWritable.get();  
7.       if (itemID < minimumItemID) {  
8.         minimumItemID = itemID;  
9.       }  
10.     }  
11.     if (minimumItemID != Long.MAX_VALUE) {  
12.       context.write(index, new VarLongWritable(minimumItemID));//将结果写入HDFS
13.     }  
14.   }