Which Operator to Use? - Instance Operators

Use this page to find the instance operator implemented by the Observable type that fits your needs:

Instance methods

Using an existing sequence	I want to change each value			map/select
	I want to pull a property off each value			pluck
	I want to be notified of values without affecting them			do/tap doOnNext/tapOnNext doOnError/tapOnError doOnCompleted/tapOnCompleted
	I want to include values	based on custom logic		filter/where
		from the start of the sequence		take
		from the start of the sequence	based on custom logic	takeWhile

		from the end of the sequence		takeLast
		until another sequence emits a value or completes		takeUntil
	I want to ignore values	altogether		ignoreElements
		from the start of the sequence		skip
		from the start of the sequence	based on custom logic	skipWhile
		from the end of the sequence		skipLast
		until another sequence emits a value		skipUntil
		that have the same value as the previous		distinctUntilChanged
		that occur too frequently		throttle
	I want to compute	the sum	of its values	sum
		the average	of its values	average
		using custom logic	and only output the final value	aggregate reduce
		using custom logic	and output the values as they are calculated	scan
	I want to wrap its messages with metadata	that describes each message		materialize
		that includes the time past since the last value		timeInterval
		that includes a timestamp		timestamp
	after a period of inactivity	I want to throw an error		timeout
	after a period of inactivity	I want to switch to another sequence		timeout
	I want ensure there is only one value	and throw an error if there are more or less than one value		single
	I want ensure there is only one value	and use the default value if there are no values		singleOrDefault
	I want to only take the first value	and throw an error if there are no values		first
		and use the default value if there are no values		firstOrDefault
		within a time period		sample
	I want to only take the last value	and error if there are no values		last
	I want to only take the last value	and use the default value if there are no values		lastOrDefault
	I want to know how many values it contains			count
	I want to know if it includes a value			contains
	I want to know if a condition is satisfied	by any of its values		any/some
	I want to know if a condition is satisfied	by all of its values		all/every
	I want to delay messages by a specific amount of time			delay
	I want to delay messages by a specific amount of time		based on custom logic	delayWithSelector
	I want to group the values	until the sequence completes		toArray toMap toSet
		using custom logic	as arrays	buffer
		using custom logic	as sequences	window
		in batches of a particular size	as arrays	bufferWithCount
		in batches of a particular size	as sequences	windowWithCount
		based on time	as arrays	bufferWithTime
		based on time	as sequences	windowWithTime
		based on time or count, whichever happens first	as arrays	bufferWithTimeOrCount
		based on time or count, whichever happens first	as sequences	windowWithTimeOrCount
		based on a key	until the sequence completes	groupBy
		based on a key	and control the lifetime of each group	groupByUntil
	I want to start a new sequence for each value	and emit the values from all sequences in parallel		flatMap/selectMany
		and emit the values from each sequence in order		concatMap/selectConcat
		and cancel the previous sequence when a new value arrives		flatMapLatest/selectSwitch
		and recursively start a new sequence for each new value		expand
		and emit values from all sequences depending for onNext, onError, and onCompleted in parallel		flatMapObserver/selectManyObserver
		and emit values from all sequences depending for onNext, onError, and onCompleted in order		concatMapObserver/selectConcatObserver
	I want to combine it with another	And be notified when both have completed		forkJoin
	I want to perform complex operations without breaking the fluent calls			let
	I want to share a subscription between multiple subscribers	using a specific subject implementation		multicast
				publish share
		and supply the last value to future subscribers		publishLast shareLast
		and replay a default or the latest value to future subscribers		publishValue shareValue
		and replay n number of values to future subscribers		replay shareReplay
	when an error occurs	I want to re-subscribe		retry
		I want to start a new sequence		catch
that depends on the error		I want to start a new sequence	catch
when it completes	I want to re-subscribe		repeat
when it completes	I want to start a new sequence		concat
when it completes or errors	I want to start a new sequence		onErrorResumeNext
when it completes, errors or unsubscribes	I want to execute a function		finally
I want to change the scheduler that routes	calls to subscribe		subscribeOn
I want to change the scheduler that routes	messages		observeOn
Using two sequences	I want to decide which to receive values from	based on which one has values first		amb
	I want to determine if their values are equal			sequenceEqual
	I want to combine their values	only when the first sequence emits, using the latest value from each		withLatestFrom
		in order	reusing the latest value when unchanged	combineLatest
		in order	using each value only once	zip
		that share overlapping “lifetime” that I choose	and be notified for each combination	join
		that share overlapping “lifetime” that I choose	and be given a sequence of “rights” for each “left”	groupJoin
	I want to include values from both			merge