该页展示执行数学或者其他覆盖Obseravble/Flowable发射的整个序列的操作符。因为这些操作符必须等待源Obseravble/Flowable 完成发射item在他们能构建他们自己的排放之前（且必须经常缓存这些item），这些操作符用在有非常长或者无限的Obseravble/Flowable序列上是非常危险的。
Outline
Mathematical Operators
averageDouble
averageFloat
max
min
sumDouble
sumFloat
sumInt
sumLong
Standard Aggregate Operators
count
reduce
reduceWith
collect
collectInto
toList
toSortedList
toMap
toMultimap
数学操作符
这些操作符是RxJava2Extensions 工程的一部分。你必须添加rxjava2-extensions模块作为你工程的依赖。它能够在http://search.maven.org找到。
注意：不像标准的RxJava 聚合器操作符，这些数学操作符返回obseravble和Flowable而不是Single 或者Maybe.
如下例子假定MathObseravble 和MathFlowable是被rxjava2-extensions模块引入的：
import hu.akarnokd.rxjava2.math.MathObservable;
import hu.akarnokd.rxjava2.math.MathFlowable;
averageDouble
Available in:
ReactiveX doumentation: http://reactivex.io/documentation/operators/average.html
计算被一个obseravble发射的平均值，且以double类型发射该平均值。
averageDouble example
Observable numbers = Observable.just(1, 2, 3);
MathObservable.averageDouble(numbers).subscribe((Double avg) -> System.out.println(avg));
// prints 2.0
averageFloat
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/average.html
计算被一个obseravble发射的平均值，且以Float类型发射该平均值。
averageFloat example
Observable numbers = Observable.just(1, 2, 3);
MathObservable.averageFloat(numbers).subscribe((Float avg) -> System.out.println(avg));
// prints 2.0
max
Available in:Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/max.html
发射被源Obseravable发射的最大值。一个Comparator能被指定且将被用于比较被Obseravable发射的元素。
max example
Observable numbers = Observable.just(4, 9, 5);
MathObservable.max(numbers).subscribe(System.out::println);
// prints 9
下面的例子指定一个Comparator去寻找源Observable最长的String
final Observable names = Observable.just("Kirk", "Spock", "Chekov", "Sulu");
MathObservable.max(names, Comparator.comparingInt(String::length))
.subscribe(System.out::println);
// prints Chekov
min
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/min.html
发射被源Observable发射的最小值。一个Comparator能被指定且将被用于比较被Observable发射的元素。
min example
Observable numbers = Observable.just(4, 9, 5);
MathObservable.min(numbers).subscribe(System.out::println);
// prints 4
sumDouble
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/sum.html
添加被Observable发射的Double值且发射这个和
sumDouble example
Observable numbers = Observable.just(1.0, 2.0, 3.0);
MathObservable.sumDouble(numbers).subscribe((Double sum) -> System.out.println(sum));
// prints 6.0
sumFloat
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/sum.html
添加被Observable发射的Float值且发射这个和
sumFloat example
Observable numbers = Observable.just(1.0F, 2.0F, 3.0F);
MathObservable.sumFloat(numbers).subscribe((Float sum) -> System.out.println(sum));
// prints 6.0
sumInt
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/sum.html
添加被Observable发射的Int值且发射这个和
sumInt example
Observable numbers = Observable.range(1, 100);
MathObservable.sumInt(numbers).subscribe((Integer sum) -> System.out.println(sum));
// prints 5050
sumLong
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/sum.html
添加被Observable发射的Long值且发射这个和
sumLong example
Observable numbers = Observable.rangeLong(1L, 100L);
MathObservable.sumLong(numbers).subscribe((Long sum) -> System.out.println(sum));
// prints 5050
标准集合操作符
注意：这些标准的集合操作符返回一个Single或Maybe因为输出item的数量最多只有一个
count
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/count.html
计算被一个Observable发射的item的数量，且以Long型返回这个值
count example
Observable.just(1, 2, 3).count().subscribe(System.out::println);
// prints 3
reduce
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/reduce.html
对每个发射的item应用一个函数,且只发射最终积累的值
reduce example
Observable.range(1, 5)
.reduce((product, x) -> product * x)
.subscribe(System.out::println);
// prints 120
reduceWith
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/reduce.html
对每个发射的item应用一个函数,且只发射最终积累的值
reduceWith example
Observable.just(1, 2, 2, 3, 4, 4, 4, 5)
.reduceWith(TreeSet::new, (set, x) -> {
set.add(x);
return set;
})
.subscribe(System.out::println);
// prints [1, 2, 3, 4, 5]
collect
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/reduce.html
收集被源Observable发射的item 到一个可变的单一的数据结构且返回一个发射该数据结构的Observable.
collect example
Observable.just("Kirk", "Spock", "Chekov", "Sulu")
.collect(() -> new StringJoiner(" \uD83D\uDD96 "), StringJoiner::add)
.map(StringJoiner::toString)
.subscribe(System.out::println);
// prints Kirk Spock Chekov Sulu
collectInto
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/reduce.html
收集被源Observable发射的item 到一个可变的单一的数据结构且返回一个发射该数据结构的Observable.
collectInto example
Observable.just("Kirk", "Spock", "Chekov", "Sulu")
.collect(() -> new StringJoiner(" \uD83D\uDD96 "), StringJoiner::add)
.map(StringJoiner::toString)
.subscribe(System.out::println);
// prints Kirk Spock Chekov Sulu
toList
**Available in:Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/to.html
从Observable中收集所有的item且发射他们为一个单一的List
toList example
Observable.just(2, 1, 3)
.toList()
.subscribe(System.out::println);
// prints [2, 1, 3]
toSortedList
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/to.html
从一个Observable中收集所有的item且发射他们为一个单一的、排好序的List
toSortedList example
Observable.just(2, 1, 3)
.toSortedList(Comparator.reverseOrder())
.subscribe(System.out::println);
// prints [3, 2, 1]
toMap
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/to.html
把Observable发射的item序列转换成一个以一个指定的key函数为key的Map
toMap example
Observable.just(1, 2, 3, 4)
.toMap((x) -> {
// defines the key in the Map
return x;
}, (x) -> {
// defines the value that is mapped to the key
return (x % 2 == 0) ? "even" : "odd";
})
.subscribe(System.out::println);
// prints {1=odd, 2=even, 3=odd, 4=even}
toMultimap
Available in: Flowable,Observable
ReactiveX doumentation: http://reactivex.io/documentation/operators/to.html
把Observable发射的item序列转换成一个Collection ，该Collection也是一个以一个指定的key函数为key的Map
toMultimap example
Observable.just(1, 2, 3, 4)
.toMultimap((x) -> {
// defines the key in the Map
return (x % 2 == 0) ? "even" : "odd";
}, (x) -> {
// defines the value that is mapped to the key
return x;
})
.subscribe(System.out::println);
// prints {even=[2, 4], odd=[1, 3]}