# Operators by Categories # This topic lists all major operators implemented by the [`Observable`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/observable.md) type by their categories, specifically: creation, conversion, combine, functional, mathematical, time, exceptions, miscellaneous, selection and primitives. ## Operators by Categories ##

Usage	Operators
Creating an observable sequence	create createWithDisposable defer generate generateWithAbsoluteTime generateWithRelativeTime range using
Converting events or asynchronous patterns to observable sequences, or between Arrays and observable sequences.	fromArray fromCallback fromNodeCallback fromEvent fromEventPattern fromPromise toArray
Combining multiple observable sequences into a single sequence.	amb prototype.amb combineLatest concat prototype.concat startWith merge prototype.merge mergeObservable repeat prototype.repeat zip prototype.zip
Functional	let publish publishLast replay
Mathemathical operators on sequences	aggregate average count max maxBy min minBy reduce sum
Time-based operations	delay interval throttle throttleWithSelector timeInterval timer timeoutWithSelector timestamp
Handling Exceptions	catch prototype.catch finally onErrorResumenext prototype.onErrorResumeNext retry
Filtering and selecting values in a sequence	elementAt elementAtOrDefault filter flatMap flatMapLatest first firstOrDefault find findIndex last lastOrDefault map pluck select selectMany selectSwitch single singleOrDefault skip skipLast skipLastWithTime skipUntil skipWhile take takeLast takeLastBuffer takeLastBufferWithTime takeLastWithTime takeWhile where
Grouping and Windowing	buffer bufferWithCount bufferWithTimeOrCount groupBy groupByUntil groupJoin join window windowWithCount windowWithTime windowWithTimeOrCount
Imperative Operators	case do doWhile for if while
Primitives	empty never return throw

## See Also ## *Reference* - [`Observable`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/observable.md) *Concepts* - [Querying Observable Sequences](querying.md)