从列表中删除重复元素 [英] Removing duplicate elements from a List

问题描述

我已经开发了一个数组列表.

I have developed an array list.

ArrayList<String> list = new ArrayList<String>();

list.add("1");
list.add("2");
list.add("3");
list.add("3");
list.add("5");
list.add("6");
list.add("7");
list.add("7");
list.add("1");
list.add("10");
list.add("2");
list.add("12");

但如上所示，它包含许多重复的元素.我想从该列表中删除所有重复项.为此，我认为首先我需要将列表转换为集合.

But as seen above it contains many duplicate elements. I want to remove all duplicates from that list. For this I think first I need to convert the list into a set.

Java 是否提供将列表转换为集合的功能?是否有其他工具可以从列表中删除重复项?

Does Java provide the functionality of converting a list into a set? Are there other facilities to remove duplicates from a list?

推荐答案

您可以通过以下方式转换为 Set:

You can convert to a Set with:

Set<String> aSet = new HashSet<String>(list);

或者您可以转换为集合并返回列表:

Or you can convert to a set and back to a list with:

list = new ArrayList<String>(new HashSet<String>(list));

然而，这两者都不太可能保持元素的顺序.为了保持顺序，您可以在迭代时使用 HashSet 作为辅助结构:

Both of these, however, are not likely to preserve the order of the elements. To preserve order, you can use a HashSet as an auxiliary structure while iterating:

List<String> list2 = new ArrayList<String>();
HashSet<String> lookup = new HashSet<String>();
for (String item : list) {
    if (lookup.add(item)) {
        // Set.add returns false if item is already in the set
        list2.add(item);
    }
}
list = list2;

在重复的情况下，只有第一次出现在结果中.如果您只想出现最后一次出现，那将是一个更棘手的问题.我会通过反转输入列表，应用上述内容，然后反转结果来解决它.

In the case of duplicates, only the first occurrence will appear in the result. If you want only the last occurrence to appear, that's a tougher problem. I'd tackle it by reversing the input list, applying the above, and then reversing the result.

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