Java8進行多個字段分組統計實現

 

// 分組統計
Map<String, Long> countMap = records.stream().collect(Collectors.groupingBy(o -> o.getProductType() + "_" + o.getCountry(), Collectors.counting()));

List<Record> countRecords = countMap.keySet().stream().map(key -> {
    String[] temp = key.split("_");
    String productType = temp[0];
    String country = temp[1];
    
    Record record = new Record();
    record.set("device_type", productType);
    record.set("location", country;
    record.set("count", countMap.get(key).intValue());
    return record;
}).collect(Collectors.toList());