Java 从集合中获取随机元素
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Get Random Element from Collection
提问by Secret
I have a Collection<Obj>how do I get a random Objfrom it?
我有一个Collection<Obj>如何从中获得随机数Obj？
I've checked the docsand there doesn't seem to be a way, since iterator is the only way to access the collection. Do I have to iterate over it to get a random object!?
我检查了文档，似乎没有办法，因为迭代器是访问集合的唯一方法。我是否必须迭代它才能获得一个随机对象！？
采纳答案by Peter Lawrey
The most efficient it to only iterate as far as you need.
最有效的方法是仅根据需要进行迭代。
public static <T> T random(Collection<T> coll) {
int num = (int) (Math.random() * coll.size());
for(T t: coll) if (--num < 0) return t;
throw new AssertionError();
}
回答by A Paul
User Collections.shuffle(list);. Then you can just get the first element. It will be random.
用户Collections.shuffle(list);. 然后你就可以得到第一个元素。这将是随机的。
or you can also do this
或者你也可以这样做
int size = list.size();
int item = new Random().nextInt(size);
list.get(item )
回答by Autocrab
private Object getRandomObject(Collection from) {
Random rnd = new Random();
int i = rnd.nextInt(from.size());
return from.toArray()[i];
}
回答by Maurice Perry
Several options (by order of efficiency):
几个选项（按效率排序）：
- use a List instead of a Collection,
- generate a random index with random.nextInt(collection.size()), get an iterator and iterate,
- generate a random index with random.nextInt(collection.size()), convert the collection into an array with toArray(), and index that array.
- 使用列表而不是集合，
- 用 random.nextInt(collection.size()) 生成一个随机索引，得到一个迭代器并迭代，
- 使用 random.nextInt(collection.size()) 生成随机索引，使用 toArray() 将集合转换为数组，并索引该数组。
回答by Witold Kaczurba
Using Lambdas you can do this quite quickly and handle the case when Collection is empty.
使用 Lambdas，您可以非常快速地完成此操作并处理 Collection 为空的情况。
public static <E> Optional<E> getRandom (Collection<E> e) {
return e.stream()
.skip((int) (e.size() * Math.random()))
.findFirst();
}
回答by RKumsher
If you don't mind a 3rd party library, the Utilslibrary has a IterableUtilsthat has a randomFrom(Iterable iterable) method that will take a Collection and return a random element from it
如果您不介意第 3 方库，Utils库有一个IterableUtils，它有一个 randomFrom(Iterable iterable) 方法，该方法将获取一个集合并从中返回一个随机元素
Collection<Object> collection = ....;
Object random = IterableUtils.randomFrom(collection);
It is in the Maven Central Repository at:
它位于 Maven 中央存储库中：
<dependency>
<groupId>com.github.rkumsher</groupId>
<artifactId>utils</artifactId>
<version>1.3</version>
</dependency>
回答by Ernest Sadykov
Solution using Google Guava Iterables.get()method:
使用谷歌番石榴Iterables.get()方法的解决方案：
private <T> T getRandomObject(Collection<T> from) {
Random rnd = new Random();
int i = rnd.nextInt(from.size());
return Iterables.get(from, i);
}
If you want to handle empty collections as well, the method with defaultValuemay be used: Iterables.get(from, i, null)
如果您还想处理空集合，可以使用with 方法defaultValue：Iterables.get(from, i, null)
