Java 8流中的arg max? [英] arg max in Java 8 streams?
问题描述
根据产生double或int值的标准的最大化,我经常需要集合的最大元素。 Streams有max()函数,需要我实现一个比较器,我觉得很麻烦。是否有更简洁的语法,例如 names.stream()。argmax(String :: length)
在以下示例中?
I often need the maximum element of a collection according to the maximization of a criterion which produces a double or int value. Streams have the max() function which requires me to implement a comparator, which I find cumbersome. Is there a more concise syntax, such as names.stream().argmax(String::length)
in the following example?
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class ArgMax
{
public static void main(String[] args)
{
List<String> names = Arrays.asList("John","Joe","Marilyn");
String longestName = names.stream().max((String s,String t)->(Integer.compare(s.length(),t.length()))).get();
System.out.println(longestName);
}
}
推荐答案
使用
String longestName = names.stream().max(Comparator.comparing(String::length)).get();
来比较某些属性上的元素(可能比这更复杂,但不必) 。
to compare elements on some property (can be more complex than that, but doesn't have to).
正如Brian在评论中建议的那样,使用可选#get()
这样做是不安全的,如果有可能流
为空。您更适合使用其中一种更安全的检索方法,例如 可选#orElse(对象)
如果没有最大值,它将为您提供一些默认值。
As Brian suggests in the comments, using Optional#get()
like this is unsafe if there's a possibility that the Stream
is empty. You'd be better suited to use one of the safer retrieval methods, such as Optional#orElse(Object)
which will give you some default value if there is no max.
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