如何使用流和&amp ;;将列表中的对象按属性分组到其他列表中Java 8？ [英] How to Group Objects in a List into other Lists by Attribute using streams & Java 8?

问题描述

我想将包含 time 属性的对象列表分组为5分钟，最好使用流和收集器。

我在StackOverflow上找到的唯一可行解决方案是计算我需要多少个间隔（子列表），将每个对象添加到这些列表中的每一个，并过滤掉那些不适合相应时间范围的对象，这不是一个很好的解决方案。

（你可以在这里找到线程：如何按Java 8中的另一个元素对List的元素进行分组）

我想到类似的东西：

  List< MyObject> list = new ArrayList< MyObject>（）; 
 ....... 
列表< List< MyObject>> grouped = list.stream（）。collect（Collectors.groupingBy（obj  - > obj.getTime（）/ intervalLength））; 
  

这当然是最好的工作。

我希望，Java 8&它的功能越来越多，我们可以为这样的问题找到一个suting解决方案。

问候，
Claas M。

编辑：
最后，我使用了@Harsh Poddar的解决方案并使用

<$ p $将地图转换为列表列表p> for（Map.Entry< Integer，List< MyObject>> entry：map.entrySet（））
list.add（entry.getValue（））;


注意：之后必须对List进行排序。

解决方案

这完全正常：

  Map< Long，< List< ;为MyObject>> grouped = ticks.stream（）。collect（Collectors.groupingBy（obj  - > obj.getTime（）/ intervalLength））; 
  

此方法将为您提供一个地图，您可以在该地图上调用.values（）来获取列表列表第一个元素将包含obj.getTime（）从0到intervalLength的元素，只要有这样的元素。第二个将包含intervalLength到intervalLength * 2，依此类推

I want to group a List of Objects containing a time attribute into 5-Minute intervals, preferably using streams and collectors.

The only possible solution I found on StackOverflow is to calculate how many intervals (sublists) I need, add every object to every one of these Lists and filter out the ones that dont fit into the respective timeframe, which is not exactly a nice solution.

(You can find the Thread here: How to group elements of a List by elements of another in Java 8)

I thought of something similar to this:

List<MyObject> list = new ArrayList<MyObject>();
.......
List<List<MyObject>> grouped = list.stream().collect(Collectors.groupingBy(obj -> obj.getTime() / intervalLength));

This of course doenst work.

I hope that, with Java 8 & its features being used more and more, we can find a suting solution for such a Problem.

Regards, Claas M.

EDIT: In the End, I used @Harsh Poddar's solution and converted the Map into a List of Lists using

for(Map.Entry<Integer, List<MyObject>> entry:map.entrySet())
  list.add(entry.getValue());

Note: The List had to be sorted afterwards.

解决方案

This works totally fine:

Map<Long,<List<MyObject>> grouped = ticks.stream().collect(Collectors.groupingBy(obj -> obj.getTime() / intervalLength));

This method will give you a map on which you may then call .values() to get the list of lists. First element will contain elements with obj.getTime() from 0 to intervalLength provided there were such elements. The second will contain from intervalLength to intervalLength*2 and so on

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