Example usage for java.util.stream Collectors reducing

Introduction

In this page you can find the example usage for java.util.stream Collectors reducing.

Prototype

public static <T> Collector<T, ?, T> reducing(T identity, BinaryOperator<T> op) 

Source Link

Document

Returns a Collector which performs a reduction of its input elements under a specified BinaryOperator using the provided identity.

Usage

From source file:com.baidu.rigel.biplatform.tesseract.isservice.search.agg.AggregateCompute.java

/**
 * ?/*from  w  ww  . ja va 2s .c  o  m*/
 * 
 * @param dataList
 *            ?
 * @param query
 *            
 * @return LinkedList<ResultRecord> ??
 */
public static List<SearchIndexResultRecord> aggregate(List<SearchIndexResultRecord> dataList, int dimSize,
        List<QueryMeasure> queryMeasures) {

    if (CollectionUtils.isEmpty(queryMeasures) || CollectionUtils.isEmpty(dataList) || dataList.size() == 1) {
        LOGGER.info("no need to group.");
        return dataList;
    }
    List<SearchIndexResultRecord> result = new ArrayList<SearchIndexResultRecord>();

    //        Set<Integer> countIndex = Sets.newHashSet();
    //        for (int i = 0 ; i < queryMeasures.size() ; i++) {
    //            if (queryMeasures.get(i).getAggregator().equals(Aggregator.COUNT)) {
    //                countIndex.add(dimSize + i);
    //            }
    //        }
    int arraySize = dataList.get(0).getFieldArraySize();

    long current = System.currentTimeMillis();
    Map<String, SearchIndexResultRecord> groupResult = dataList.parallelStream()
            .collect(Collectors.groupingByConcurrent(SearchIndexResultRecord::getGroupBy, Collectors
                    .reducing(new SearchIndexResultRecord(new Serializable[arraySize], null), (x, y) -> {
                        SearchIndexResultRecord var = new SearchIndexResultRecord(new Serializable[arraySize],
                                y.getGroupBy());
                        try {
                            for (int i = 0; i < dimSize; i++) {
                                var.setField(i, y.getField(i));
                            }
                            int index = dimSize;
                            for (int i = 0; i < queryMeasures.size(); i++) {
                                QueryMeasure measure = queryMeasures.get(i);
                                index = i + dimSize;
                                var.setField(i + dimSize, Aggregate.aggregate(x.getField(index),
                                        y.getField(index), measure.getAggregator()));
                            }
                        } catch (Exception e) {
                            e.printStackTrace();
                            throw new RuntimeException(e);
                        }
                        return var;
                    })));
    LOGGER.info("group agg(sum) cost: {}ms!", (System.currentTimeMillis() - current));
    result.addAll(groupResult.values());

    return result;
}

---