RepeatCount

RepeatCountAggregate 实现了“重复计数”聚合；即重复出现 N 次或更多次的项的数量。

类定义

    public static class RepeatCountAggregate implements Aggregate
    {
        static class Counter 
        {
            int value;
            Counter(int val) 
            {
                value = val;
            }
        }
         
        public void initialize(Object val) 
        {
            accumulate(val);
        }
 
        public void accumulate(Object val) 
        {
            Counter counter = occ.get(val);
            if (counter == null) 
            {
                counter = new Counter(1);
                occ.put(val, counter);
            } else {
                counter.value += 1;
            }
            if (counter.value == minOccurrences) 
            {
                count += 1;
            }
        }
 
        public Object result() 
        {
            return new Long(count);
        }
         
        public void merge(Aggregate other) 
        {
            for (Map.Entry<Object,Counter> pair : ((RepeatCountAggregate)other).occ.entrySet()) 
            {
                Object key = pair.getKey();
                Counter counter = occ.get(key);
                if (counter == null) 
                {
                    counter = pair.getValue();
                    occ.put(key, counter);
                    if (counter.value >= minOccurrences) 
                    {
                        count += 1;
                    }
                } else {
                    int oldValue = counter.value;
                    counter.value += pair.getValue().value;
                    if (oldValue < minOccurrences && counter.value >= minOccurrences) 
                    {
                        count += 1;
                    }
                }
            }
        }
         
        /**
        * Constructor of aggregate
        * @param minOccurrences minimal number of occurrences
        */
        public RepeatCountAggregate(int minOccurrences) 
        {
            this.minOccurrences = minOccurrences;
        }
         
        HashMap<Object,Counter> occ = new HashMap<Object,Counter>();
        int minOccurrences;
        long count;
    }