java8 Stream reduce 集合分组并递减

最新推荐文章于 2024-06-27 09:15:25 发布

即使再小的帆也能远航

最新推荐文章于 2024-06-27 09:15:25 发布

阅读量1k

点赞数

文章标签： java

本文链接：https://blog.youkuaiyun.com/guo_jee/article/details/123627840

版权

java8 Stream reduce 集合分组并递减

 Map<String, Object> map1 = new HashMap<>();
        map1.put("dev", "fan1");
        map1.put("kwh", 50d);
        Map<String, Object> map2 = new HashMap<>();
        map2.put("dev", "fan1");
        map2.put("kwh", 50d);
        Map<String, Object> map3 = new HashMap<>();
        map3.put("dev", "fan3");
        map3.put("kwh", 50d);
        Map<String, Object> map4 = new HashMap<>();
        map4.put("dev", "fan1");
        map4.put("kwh", 100D);
        List<Map<String, Object>> list = new ArrayList<>();
        list.add(map2);
        list.add(map1);
        list.add(map3);
        list.add(map4);


        if (CollectionUtils.isNotEmpty(list)) {
            List<Map<String, Object>> result = new ArrayList<>();
            list.stream().collect(Collectors.groupingBy(m-> m.get("dev").toString(), Collectors.toList())).
                    forEach(
                            (id, value) -> {
                                   //如果大于两天才会执行 按照自己的
                                   if (value.size()>=2) {
                                       value.stream().reduce((a, b) ->
                                       {
                                           Map<String, Object> map = new HashMap();
                                           if (!b.isEmpty()) {
                                               map.put("dev", a.get("dev").toString());
                                               map.put("kwh", (Double) a.get("kwh") - (Double) b.get("kwh"));
                                           }
                                           return map;

                                       }).ifPresent(result::add);

                                   }
                            });
            System.out.println(result);
        }

结果: [{dev=fan1, kwh=-100.0}]