blocks|key|4618821|text|根据Lucas的说法，你可以像这样创建一个Array类的扩展：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4618822|extension+Array+{
++++func+randomItem()+->+Element?+{
++++++++if+isEmpty+{+return+nil+}
++++++++let+index+=+Int(arc4random_uniform(UInt32(self.count)))
++++++++return+self[index]
++++}
}|code-block|syntax|javascript|4618823|例如：|4618824|let+myArray+=+[1,+2,+3,+4,+5,+6,+7,+8,+10,+12,+14,+16]
let+myItem+=+myArray.randomItem()+//+Note:+myItem+is+an+Optional<Int>|4618825|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Riffing on what Lucas said, you could create an extension to the Array class like this:

<pre><code>extension Array {
 func randomItem() -&gt; Element? {
 if isEmpty { return nil }
 let index = Int(arc4random_uniform(UInt32(self.count)))
 return self[index]
 }
}
</code></pre>

For example: 

<pre><code>let myArray = [1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16]
let myItem = myArray.randomItem() // Note: myItem is an Optional&lt;Int&gt;
</code></pre>

blocks|key|112762|text|你也可以对扩展使用Swift内置的random()函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|112763|extension+Array+{
++++func+sample()+->+Element+{
++++++++let+randomIndex+=+Int(rand())+%25+count
++++++++return+self[randomIndex]
++++}
}

let+array+=+[1,+2,+3,+4]

array.sample()+//+2
array.sample()+//+2
array.sample()+//+3
array.sample()+//+3

array.sample()+//+1
array.sample()+//+1
array.sample()+//+3
array.sample()+//+1|code-block|syntax|javascript|112764|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use Swift's built-in random() function as well for the extension: 

<pre><code>extension Array {
 func sample() -&gt; Element {
 let randomIndex = Int(rand()) % count
 return self[randomIndex]
 }
}

let array = [1, 2, 3, 4]

array.sample() // 2
array.sample() // 2
array.sample() // 3
array.sample() // 3

array.sample() // 1
array.sample() // 1
array.sample() // 3
array.sample() // 1
</code></pre>

blocks|key|4619008|text|另一个Swift+3建议|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4619009|private+extension+Array+{
++++var+randomElement:+Element+{
++++++++let+index+=+Int(arc4random_uniform(UInt32(count)))
++++++++return+self[index]
++++}
}|code-block|syntax|javascript|4619010|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Another Swift 3 suggestion

<pre><code>private extension Array {
 var randomElement: Element {
 let index = Int(arc4random_uniform(UInt32(count)))
 return self[index]
 }
}
</code></pre>

blocks|key|4618918|text|跟随其他人的回答，但支持Swift+2。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4618919|Swift+1.x|4618920|extension+Array+{
++++func+sample()+->+T+{
++++++++let+index+=+Int(arc4random_uniform(UInt32(self.count)))
++++++++return+self[index]
++++}
}|code-block|syntax|javascript|4618921|Swift+2.x|4618922|extension+Array+{
++++func+sample()+->+Element+{
++++++++let+index+=+Int(arc4random_uniform(UInt32(self.count)))
++++++++return+self[index]
++++}
}|4618923|例如：|4618924|let+arr+=+[2,+3,+5,+7,+9,+11,+13,+17,+19,+23,+29,+31]
let+randomSample+=+arr.sample()|4618925|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Following others answer but with Swift 2 support.

<h2>Swift 1.x</h2>

<pre><code>extension Array {
 func sample() -&gt; T {
 let index = Int(arc4random_uniform(UInt32(self.count)))
 return self[index]
 }
}
</code></pre>

<h2>Swift 2.x</h2>

<pre><code>extension Array {
 func sample() -&gt; Element {
 let index = Int(arc4random_uniform(UInt32(self.count)))
 return self[index]
 }
}
</code></pre>

E.g.: 

<pre><code>let arr = [2, 3, 5, 7, 9, 11, 13, 17, 19, 23, 29, 31]
let randomSample = arr.sample()
</code></pre>

blocks|key|112794|text|使用检查空数组的替代函数实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|112795|func+randomArrayItem<T>(array:+[T])+->+T?+{
++if+array.isEmpty+{+return+nil+}
++let+randomIndex+=+Int(arc4random_uniform(UInt32(array.count)))
++return+array[randomIndex]
}

randomArrayItem([1,2,3])|code-block|syntax|javascript|112796|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

An alternative functional implementation with check for empty array.

<pre><code>func randomArrayItem&lt;T&gt;(array: [T]) -&gt; T? {
 if array.isEmpty { return nil }
 let randomIndex = Int(arc4random_uniform(UInt32(array.count)))
 return array[randomIndex]
}

randomArrayItem([1,2,3])
</code></pre>

blocks|key|4619020|text|Swift+3|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4619021|导入GameKit|4619022|func+getRandomMessage()+->+String+{

++++let+messages+=+["one",+"two",+"three"]

++++let+randomNumber+=+GKRandomSource.sharedRandom().nextInt(upperBound:+messages.count)

++++return+messages[randomNumber].description

}|code-block|syntax|javascript|4619023|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Swift 3 

import GameKit

<pre><code>func getRandomMessage() -&gt; String {

 let messages = ["one", "two", "three"]

 let randomNumber = GKRandomSource.sharedRandom().nextInt(upperBound: messages.count)

 return messages[randomNumber].description

}
</code></pre>

blocks|key|4618966|text|我发现使用GameKit的GKRandomSource.sharedRandom()最适合我。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4618967|import+GameKit

let+array+=+["random1",+"random2",+"random3"]

func+getRandomIndex()+->+Int+{
++++let+randomNumber+=+GKRandomSource.sharedRandom().nextIntWithUpperBound(array.count)
++++return+randomNumber|code-block|syntax|javascript|4618968|或者，您可以返回所选随机索引处的对象。确保函数首先返回一个字符串，然后再返回数组的索引。|4618969|++++return+array[randomNumber]|4618970|简短且切中要害。|4618971|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I find using GameKit's GKRandomSource.sharedRandom() works best for me.

<pre><code>import GameKit

let array = ["random1", "random2", "random3"]

func getRandomIndex() -&gt; Int {
 let randomNumber = GKRandomSource.sharedRandom().nextIntWithUpperBound(array.count)
 return randomNumber
</code></pre>

or you could return the object at the random index selected. Make sure the function returns a String first, and then return the index of the array.

<pre><code> return array[randomNumber]
</code></pre>

Short and to the point.

blocks|key|112970|text|现在Collection上有一个内置的方法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|112971|let+foods+=+["",+"",+"",+""]
let+myDinner+=+foods.randomElement()|code-block|syntax|javascript|112972|如果你想从一个集合中提取最多n个随机元素，你可以添加一个这样的扩展：|112973|extension+Collection+{
++++func+randomElements(_+count:+Int)+->+[Element]+{
++++++++var+shuffledIterator+=+shuffled().makeIterator()
++++++++return+(0..<count).compactMap+{+_+in+shuffledIterator.next()+}
++++}
}|112974|如果希望它们是唯一的，可以使用Set，但集合的元素必须符合Hashable协议：|112975|extension+Collection+where+Element:+Hashable+{
++++func+randomUniqueElements(_+count:+Int)+->+[Element]+{
++++++++var+shuffledIterator+=+Set(shuffled()).makeIterator()
++++++++return+(0..<count).compactMap+{+_+in+shuffledIterator.next()+}
++++}
}|112976|entityMap^0|2|A|0|0|E|1|0|0|F|3|T|8|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|T|$]]

There is a built-in method on <code>Collection</code> now:

<pre><code>let foods = ["", "", "", ""]
let myDinner = foods.randomElement()
</code></pre>

If you want to extract up to <code>n</code> random elements from a collection you can add an extension like this one:

<pre><code>extension Collection {
 func randomElements(_ count: Int) -&gt; [Element] {
 var shuffledIterator = shuffled().makeIterator()
 return (0..&lt;count).compactMap { _ in shuffledIterator.next() }
 }
}
</code></pre>

And if you want them to be unique you can use a <code>Set</code>, but the elements of the collection must conform to the <code>Hashable</code> protocol:

<pre><code>extension Collection where Element: Hashable {
 func randomUniqueElements(_ count: Int) -&gt; [Element] {
 var shuffledIterator = Set(shuffled()).makeIterator()
 return (0..&lt;count).compactMap { _ in shuffledIterator.next() }
 }
}
</code></pre>

Suppose I have an array and I want to pick one element at random.

What would be the simplest way to do this?

The obvious way would be <code>array[random index]</code>. But perhaps there is something like ruby's <code>array.sample</code>? Or if not could such a method be created by using an extension?

Pick a random element from an array

假设我有一个数组，我想随机选取一个元素。做这件事最简单的方法是什么？最明显的方法就是array[random index]。但也许有像ruby的array.sample这样的东西？或者，如果不是，可以使用扩展来创建这样的方法吗？

问从数组中选取一个随机元素
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