AggregatorMapper的输入是<key, value=TopKStringPatterns>，TopKStringPatterns是一个存储<Pair<List<String>,Long>>类型的列表，List<String>类型元素记录了每一个key=item对应的频繁模式，Long类型元素记录了支持度。
1 /** 2 * 3 * outputs the pattern for each item in the pattern, so that reducer can group them 4 * and select the top K frequent patterns 5 * 6 */ 7 public class AggregatorMapper extends Mapper<Text,TopKStringPatterns,Text,TopKStringPatterns> { 8 9 @Override 10 protected void map(Text key, TopKStringPatterns values, Context context) throws IOException, 11 InterruptedException { 12 for (Pair<List<String>,Long> pattern : values.getPatterns()) { 13 for (String item : pattern.getFirst()) { 14 List<Pair<List<String>,Long>> patternSingularList = Lists.newArrayList(); 15 patternSingularList.add(pattern); 16 context.setStatus("Aggregator Mapper:Grouping Patterns for " + item); 17 context.write(new Text(item), new TopKStringPatterns(patternSingularList)); 18 } 19 } 20 21 } 22 }
AggregatorReducer汇总了所有Key相同的item，然后按照支持度递减排序，最终输出Top K个频繁模式。