使用 Java 8 從（嵌套列表）列表列表中獲取列表的最大和最小總和

Question

我正在檢查這些問題，但它沒有回答我的問題

如何使用 Java 從對象列表中獲取最小值和最大值 8
在 Java 8 中查找列表的最大值、最小值、總和和平均值

我的問題我有嵌套列表，我想獲得一個列表。

我有這個 class：

public class Competitor {
  private final int type;
  private final String name;
  private final int power;

  public Competitor(int type, String name, int power) {
    this.type = type;
    this.name = name;
    this.power = power;
  }

  public int getType() {
    return type;
  }

  public String getName() {
    return name;
  }

  public int getPower() {
    return power;
  }

  @Override
  public String toString() {
    return "Competitor{" + "type=" + type + ", name=" + name + ", power=" + power + "} ";
  }

}

現在我有一個List<List<Competitor>>像：

List<List<Competitor>> anotherListOfListCompetitor = new ArrayList<>();
anotherListOfListCompetitor.add(new ArrayList<>(
    Arrays.asList(new Competitor(1, "Cat 00", 93), new Competitor(2, "Dog 18", 40), new Competitor(3, "Pig 90", 90)))); //93 + 40 + 90 = 223

anotherListOfListCompetitor.add(new ArrayList<>(
    Arrays.asList(new Competitor(1, "Cat 23", 20), new Competitor(2, "Dog 30", 68), new Competitor(3, "Pig 78", 32)))); //20 + 68 + 32 = 120

anotherListOfListCompetitor.add(new ArrayList<>(
    Arrays.asList(new Competitor(1, "Cat 10", 11), new Competitor(4, "Cow 99", 90)))); //11 + 90 = 101

現在，我想獲得具有最小power屬性總和的List<Competitor> <Competitor> 和具有最大總和的其他List<Competitor> 。

我知道減少...

List<Competitor> someListCompetitor = //populate the list

int sumPower = someListCompetitor.stream()
    .map(competitor -> competitor.getPower())
    .reduce(0, (a, b) -> a + b);

但是List<List<Competitor>>是否有可能獲得具有最小sumPower的minListCompetitor和具有最大anotherListCompetitor的sumPower ？

List<Competitor> minListCompetitor = anotherListOfListCompetitor
    .stream()... // which sum power is 101


List<Competitor> maxListCompetitor = anotherListOfListCompetitor
    .stream()... // which sum power is 223

如何獲取這些列表？

Answer 1

你可以使用這個：

List<Competitor> minListCompetitor = anotherListOfListCompetitor.stream()
        .min(Comparator.comparingInt(l -> l.stream().mapToInt(Competitor::getPower).sum()))
        .orElse(Collections.emptyList());

List<Competitor> maxListCompetitor = anotherListOfListCompetitor.stream()
        .max(Comparator.comparingInt(l -> l.stream().mapToInt(Competitor::getPower).sum()))
        .orElse(Collections.emptyList());

這將返回列表中總和的.min() / .max() 。 它使用您提供的代碼的簡化版本來計算總和。

如果你想在沒有找到最大值的情況下拋出異常，你可以使用.orElseThrow() 。