[英]Find the min and max number from a Collection using Java streams
Below is the code snippet which, as expected, is failing at compile time. 下面是代码片段,正如预期的那样,在编译时失败。
What I really want to do is to find the min and max from all the lists using streams. 我真正想要做的是使用流找到所有列表中的最小值和最大值。
public class Delete {
public static void main(String[] args) {
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 677, 0);
List<Integer> list1 = Arrays.asList(11, 12, 23, 34, 25, 77);
List<Integer> list2 = Arrays.asList(12, 21, 30, 14, 25, 67);
List<Integer> list3 = Arrays.asList(41, 25, 37, 84, 95, 7);
List<List<Integer>> largeList = Arrays.asList(list, list1, list2, list3);
System.out.println(largeList.stream().max(Integer::compare).get());
System.out.println(largeList.stream().min(Integer::compare).get());
}
}
You have to flatten the elements of all the List
s into a single Stream<Integer>
in order for your code to work : 您必须将所有List
的元素展平为单个Stream<Integer>
,以便您的代码可以工作:
System.out.println(largeList.stream().flatMap(List::stream).max(Integer::compare).get());
System.out.println(largeList.stream().flatMap(List::stream).min(Integer::compare).get());
This is not very efficient, though, since you process the List
s twice in order to find both min
and max
, and you can get the same data (and more) in a single processing by using IntStream::summaryStatistics()
: 但是,这不是很有效,因为您处理List
两次以便同时找到min
和max
,并且您可以通过使用IntStream::summaryStatistics()
在单个处理中获得相同的数据(和更多IntStream::summaryStatistics()
:
IntSummaryStatistics stats = largeList.stream().
.flatMap(List::stream)
.mapToInt(Integer::intValue)
.summaryStatistics();
System.out.println(stats.getMin());
System.out.println(stats.getMax());
尝试这个:
largeList.stream().flatMap(List::stream).max(Integer::compare).get();
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