筛选具有共同特征的对象

Question

我需要找到我的集合是否包含相同或超过5个元素的公共变量，并找到这些元素。我这样做：

        cards.stream().filter(card -> cards.stream().filter(card1 -> card.getSuit() == card1.getSuit()).count() >= CombinationConstant.CARD_COUNT)
                .collect(Collectors.toList());

但是你认为把另一个流放进去过滤是不好的做法。

Answer 1

我不知道它是否比你的实现效率高。但这是方法之一：

List<String> cards = List.of("a","b","aa","bb","cc");
int CARD_COUNT = 3;
    
Map<Integer, Long> counted = cards.stream()
    .collect(Collectors.groupingBy((String i)-> i.length() , Collectors.counting()));
System.out.println("all counted: " + counted);
        
Map<Integer, Long> result = counted.entrySet().stream()
    .filter(k -> counted.get(k.getKey()) >= CARD_COUNT)
    .collect(Collectors.toMap(x -> x.getKey(), x1 -> x1.getValue()));;
System.out.println("filtered " + result);

输出：

all counted: {1=2, 2=3}
filtered {2=3}