从Arraylist< String>获取重复值.然后将这些项目放在另一个Arraylist中 [英] get the duplicates values from Arraylist<String> and then get those items in another Arraylist

问题描述

我有一个arraylist，其中包含一些重复的值，我想将这些值收集到另一个Arraylist中. 喜欢

I have an arraylist which contains some values with duplicates i want to collect those values into another Arraylist.... like

 Arraylist<String> one;   //contains all values with duplicates
  one.add("1");
  one.add("2");
  one.add("2");
  one.add("2");

在这里，我想在另一个arraylist中获取所有重复值...

Here, I want to get all the duplicates values in another arraylist...

Arraylist<String> duplicates;    //contains all duplicates values which is 2.

我想要那些大于或等于3的值.

I want those values which counts greater or equals 3.....

当前，我对此没有任何解决方案，请帮助我找出答案

Currently, I don't have any solution for this please help me to find out

推荐答案

您可以为此使用一个集合:

You can use a set for this:

Set<String> set = new HashSet<>();
List<String> duplicates = new ArrayList<>();

for(String s: one) {
    if (!set.add(s)) {
        duplicates.add(s);
    }
}

您只需将所有元素添加到集合中即可.如果方法add()返回false，则表示该元素未添加到集合中，即该元素已经存在.

You just keep adding all the elements to the set. If method add() returns false, this means the element was not added to set i.e it already exists there.

输入:[1, 3, 1, 3, 7, 6]

重复:[1, 3]

已编辑

对于等于或大于3的值，您可以像这样使用流来做到这一点:

For the value which counts 3 or greater, you can use streams to do it like so:

List<String> collect = one.stream()
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
            .entrySet()
            .stream()
            .filter(e -> e.getValue() >= 3)
            .map(Map.Entry::getKey)
            .collect(Collectors.toList());

基本上，您是在地图中收集初始列表的，其中key是字符串，而value是计数.然后，您可以过滤此地图以获取计数值大于3的值，并将其收集到结果列表中

Basically you collect you initial list in a map, where key is the string and value is the count. Then you filter this map for values that have count greater than 3, and collect it to the result list

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