是否可以按功能对流进行分组和分组? [英] Can i partition a stream combining with the grouping by functionality?

问题描述

我正在对流进行分组和划分，如下所示:

I am grouping and partioning a stream as follows:

// Partioning
Map<Boolean, List<Person>> partitioned = persons.stream().
                                          collect(Collectors.partitioningBy(p -> p.getAge() > 20));

// Grouping
Map<String, List<Person>> grouped = persons.stream()
                                .collect(Collectors.groupingBy(p -> p.getCity()));

有没有办法我可以将两者结合起来?我尝试在partioningBy内使用groupingBy两者结合使用，但没有把事情做对.有什么建议吗?

Is there a way i can combine both of these? I tried combining both with using groupingBy inside partioningBy, but did not get the things right. Any suggestion?

预期结果是对姓名以P开头的人员进行划分，并按年龄分组. 这是人员列表:

The expected result is the partition the persons with those whose name starts with P and group them by age. Here is the persons list:

List<Person> persons = Arrays.asList(
            new Person("Max", 18),
            new Person("Peter", 23),
            new Person("Pamela", 23),
            new Person("David", 12),
            new Person("Pam", 12)); 

推荐答案

我尝试了以下操作，并了解了它的工作原理.

I tried the following and somhow it worked.

Map<Boolean, Map<Object, List<Person>>> rr = persons.stream()
                                            .collect(Collectors.partitioningBy(p -> p.name.startsWith("P"), 
                                                    Collectors.groupingBy(p -> p.age > 20)));

输出符合预期

rr = {false={false=[Max, David]}, true={false=[Pam], true=[Peter, Pamela]}}

但是，我不确定这是否是有效的方法.有什么建议吗?

But, i am not sure is it the efficient way to do this. Any suggestions?

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