过滤和条件操作

从源可观察序列中选择性地发射元素的操作。

filter

仅从符合指定条件的可观察序列中发出这些元素。

let disposeBag = DisposeBag()

Observable.of(
    "🐱", "🐰", "🐶",
    "🐸", "🐱", "🐰",
    "🐹", "🐸", "🐱")
    .filter {
        $0 == "🐱"
    }
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)

distinctUntilChanged

抑制可观察序列发出的序列重复元素。

let disposeBag = DisposeBag()

Observable.of("🐱", "🐷", "🐱", "🐱", "🐱", "🐵", "🐱")
    .distinctUntilChanged()
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)    //🐱🐷🐱🐵🐱

elementAt

仅在可观察序列中发出的所有元素的指定索引中释放元素。

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .elementAt(3)
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)   //   🐸

single

只发出可观察序列发出的第一个元素（或满足条件的第一个元素）。如果可观察序列不是恰好发射一个元素，（多个满足条件的）则抛出一个错误。

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .single()
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)

加条件

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .single { $0 == "🐸" }
    .subscribe { print($0) }
    .disposed(by: disposeBag)   //  next(🐸)   completed

Observable.of("🐱", "🐰", "🐶", "🐱", "🐰", "🐶")
    .single { $0 == "🐰" }
    .subscribe { print($0) }
    .disposed(by: disposeBag)     // next(🐰) error(Sequence contains more than one element.)

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .single { $0 == "🔵" }
    .subscribe { print($0) }
    .disposed(by: disposeBag)  //  error(Sequence doesn't contain any elements.)

take

仅从可观察序列的开头发出指定数量的元素

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .take(3)
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)  //     🐱🐰🐶

takeLast

仅从可观察序列的结尾发出指定数量的元素。

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .takeLast(3)
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)  //   🐸🐷🐵

takeWhile

只要指定的条件求值为true，则从可观察序列的开头发出元素。

let disposeBag = DisposeBag()

Observable.of(1, 2, 3, 4, 5, 6)
    .takeWhile { $0 < 4 }
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)  // 1 2 3

takeUntil

从源可观察序列中释放元素，直到引用可观察序列发出元素结束（发照发，有人来了就不发了）

let disposeBag = DisposeBag()

let sourceSequence = PublishSubject<String>()
let referenceSequence = PublishSubject<String>()

sourceSequence
    .takeUntil(referenceSequence)
    .subscribe { print($0) }
    .disposed(by: disposeBag)

sourceSequence.onNext("🐱")
sourceSequence.onNext("🐰")
sourceSequence.onNext("🐶")

referenceSequence.onNext("🔴")

sourceSequence.onNext("🐸")
sourceSequence.onNext("🐷")
sourceSequence.onNext("🐵")   // next(🐱)  next(🐰)  next(🐶)  completed

skip

禁止从可观察序列的开头释放指定数量的元素。

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .skip(2)
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)  // 🐶🐸🐷🐵

shipWhile

禁止从符合指定条件的可观察序列的开头发出元素。

let disposeBag = DisposeBag()

Observable.of(1, 2, 3, 4, 5, 6)
    .skipWhile { $0 < 4 }
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)   // 4 5 6

skipWhileWithIndex

禁止从符合指定条件的可观察序列的开头发出元素，并发出剩余的元素。闭包可用通过每个元素的索引。

let disposeBag = DisposeBag()

Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
    .skipWhileWithIndex { element, index in
        index < 3
    }
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)  //  🐸🐷🐵

skipUntil

禁止从源可观察序列中释放元素，直到引用可观察序列发出元素。

let disposeBag = DisposeBag()

let sourceSequence = PublishSubject<String>()
let referenceSequence = PublishSubject<String>()

sourceSequence
    .skipUntil(referenceSequence)
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)

sourceSequence.onNext("🐱")
sourceSequence.onNext("🐰")
sourceSequence.onNext("🐶")

referenceSequence.onNext("🔴")

sourceSequence.onNext("🐸")
sourceSequence.onNext("🐷")
sourceSequence.onNext("🐵")  // 🐸🐷🐵

算术和集合操作