如何过滤动态嵌套列表对象Java 8 [英] How to filter dynamically nested list object java 8

问题描述

如何过滤动态嵌套列表对象Java 8

How to filter dynamically nested list object java 8

示例:

class Items {
    List<Mobile> mobiles;
}

class Mobile{
    String mName;
    List<Plans> plans;
}

class Plans{
    String planId;
    String planName;
}

因此，我有3个移动设备(移动设备将是动态3或4..etc)，每个移动设备上都有多个计划.如何为每个移动设备动态过滤通用计划?

So, I have 3 mobiles (mobiles will be dynamic 3 or 4..etc) with multiple plans on each mobile device. How to dynamically filter common plan for each mobile device ?

Items:
    M1 - P1,P2,P3,P4
    M2 - P4,P5,P6,P1,P8,P2
    M3 - P7,P2,P4,P1,P8,P9,P10

结果:

Items:
    M1 - P1,P2,P4
    M2 - P1,P2,P4
    M3 - P1,P2,P4

推荐答案

Items中的一种用于获取所有手机通用计划的方法可能看起来像:

A method inside Items to get all plans common to all mobiles might look like:

public List<Plan> getCommonPlans() {
    return mobiles.stream().flatMap(Mobile::streamPlans).distinct()
        .filter(p -> mobiles.stream().allMatch(m -> m.hasPlan(p)))
        .collect(Collectors.toList());
}

这假定Mobile.streamPlans和Mobile.hasPlan方法非常简单.

this assumes Mobile.streamPlans and Mobile.hasPlan methods which are pretty trivial.

一种略有不同的方法，更有效，但可能不是那么直观，它是对计划进行计数，并过滤计数等于移动台数量的计划:

A slightly different method, more efficient but perhaps not so intuitive, is to count the plans and filter for ones that have counts equal to number of mobiles:

    return mobiles.stream().flatMap(Mobile::streamPlans)
        .collect(Collectors.groupingBy(m -> m, Collectors.counting())
        .entrySet().stream()
        .filter(e -> e.getValue() == mobiles.size())
        .map(Map.Entry::getKey)
        .collect(Collectors.toList());

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