python,scala,java中的map,reduce和filter

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1,python中的map,reduce,filter使用

>>> a=[1,2,3,5]>>> map(lambda x:x+x,a)[2, 4, 6, 10]>>> map(lambda x:2*x,a)[2, 4, 6, 10]>>> reduce(lambda x,y:x*y,a)30>>> filter(lambda x : x%2,a)[1, 3, 5]

2,scala中的map,reduce,filter使用

scala> val list2 = 1 to 10 toListlist2: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)scala> list2.map(x=>x*x)res13: List[Int] = List(1, 4, 9, 16, 25, 36, 49, 64, 81, 100)scala> list2.map(math.pow(_,2))res14: List[Double] = List(1.0, 4.0, 9.0, 16.0, 25.0, 36.0, 49.0, 64.0, 81.0, 100.0)scala>  val sum = (x:Int, y:Int) => {x + y}sum: (Int, Int) => Int = <function2>scala> list2.reduce(sum)res15: Int = 55scala> list2.reduce(_+_)res16: Int = 55scala> list2.sumres17: Int = 55scala> list2.filter( _ % 2 != 0)res19: List[Int] = List(1, 3, 5, 7, 9)scala> list2.filterNot( _ % 2 != 0)res20: List[Int] = List(2, 4, 6, 8, 10)

3,java中的map,reduce,filter使用(java8新特性)

final List<Integer> numbers = Arrays.asList(1, 2, 3, 4);        final List<Integer> doubleNumbers = numbers.stream()                 .map(number -> number * 2)                .collect(Collectors.toList());        System.out.println(doubleNumbers);                final Optional<Integer> sum = numbers.stream()                .reduce((a, b) -> a + b);        sum.orElseGet(() -> 0);        System.out.println(sum.get());                final List<Integer> filterNumbers = numbers.stream().filter(number -> number % 2 == 0)                .collect(Collectors.toList());        System.out.println(filterNumbers);

编译执行查看结果：

D:\>javac Test.javaD:\>java Test[2, 4, 6, 8]10[2, 4]

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