从 ArrayList 中获取重复项的数量 [英] Get number of duplicates from ArrayList

问题描述

例如，假设我有一个 ArrayList 可以包含以下值:

For example, say I have an ArrayList that could contain the following values:

x
x
x
y
y

现在我要检索的是 x 和 x 的数量，我希望能够区分我所拥有的，或者 x 或 y 因为实际上，我可以在 ArrayList 中有任何对象，而且我必须能够区分它们.

Now what I want to retrieve is the number of x and x and I want to be able to differentiate what I have, either x or y because in actuality, I could have any object in the ArrayList and I have to be able to tell them apart.

我想做的是首先将 ArrayList 转换为 LinkedHashSet，这将保持排序并删除重复项，因此我只有 x 和 y 但是我如何获得每个的数量并将其与正确的元素相关联?

What I was thinking of doing was first converting the ArrayList into a LinkedHashSet, which would keep the ordering and remove the duplicates so I would just have x and y But how would I get the number of each and associate it with the proper element?

总的来说，我想要做的是能够编写一个 toString 方法，让我输出:

Overall what I want to do is to be able to write a toString method that will let me output:

x3y2

但不知道 x 和 y 是元素，因为它们可能是其他类似 z 或 w.

But without knowing that x and y are the elements because they could have been something else like z or w.

推荐答案

查看 google guava 中的 Multiset:http://docs.guava-libraries.googlecode.com/git-history/v11.0.2/javadoc/com/google/common/collect/Multiset.html

Check out the Multiset in google guava: http://docs.guava-libraries.googlecode.com/git-history/v11.0.2/javadoc/com/google/common/collect/Multiset.html

示例:

Multiset<String> strings = HashMultiset.create(arrayList);
int countX = strings.count("x"); // the count of x

可以在 Guava wiki 上找到更多示例.

More examples can be found on the Guava wiki.

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