RxJava기준 Operator임.
- ignoreElements, elementAt, filter, skip, skipWhile, skipUntil, take, takeWhile, enumerated, takeUntil, distinctUntilChanged
- toArray, map, enumerated, flatMap, flapMapLatest, materialize, dematerialize, unwrap
- startWith, concat, concatMap, merge, merge(maxConcurrent), combineLatest
- zip, withLatestFrom, sample, amb, switchLatest, reduce, scan
- replay, replayAll, buffer, window, delaySubscription, interval, timer, timeout