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
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
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	average
using custom logic	and only output the final value	aggregate reduce
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
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
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
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
by all of its values	all/every
I want to delay messages by a specific amount of time		delay
based on custom logic	delayWithSelector
I want to group the values	until the sequence completes	toArray toMap toSet
using custom logic	as arrays	buffer
as sequences	window
in batches of a particular size	as arrays	bufferWithCount
as sequences	windowWithCount
based on time	as arrays	bufferWithTime
as sequences	windowWithTime
based on time or count, whichever happens first	as arrays	bufferWithTimeOrCount
as sequences	windowWithTimeOrCount
based on a key	until the sequence completes	groupBy
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	catch
when it completes	I want to re-subscribe	repeat
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
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
using each value only once	zip
that share overlapping “lifetime” that I choose	and be notified for each combination	join
and be given a sequence of “rights” for each “left”	groupJoin
I want to include values from both	merge

See Also ##

Reference

• Observable

Concepts

• Querying Observable Sequences

• Operators By Category