如何使用流和& ;;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。
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.
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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