# Instance Operators
Use this page to find the instance operator implemented by the [`Observable`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/observable.md) type that fits your needs:
| Instance methods | | | |
| --------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- |
| Using an existing sequence | I want to change each value | [map/select](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/select.html) | |
| I want to pull a property off each value | [pluck](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/pluck.html) | | |
| 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](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/filter.html) | |
| from the start of the sequence | | [take](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/take.html) | |
| based on custom logic | [takeWhile](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/takewhile.html) | | |
| | | | |
| from the end of the sequence | [takeLast](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/takelast.html) | | |
| until another sequence emits a value or completes | [takeUntil](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/takeuntil.html) | | |
| I want to ignore values | altogether | [ignoreElements](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/ignoreelements.html) | |
| from the start of the sequence | | [skip](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/skip.html) | |
| based on custom logic | [skipWhile](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/skipwhile.html) | | |
| from the end of the sequence | [skipLast](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/skiplast.html) | | |
| until another sequence emits a value | [skipUntil](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/skipuntil.html) | | |
| that have the same value as the previous | [distinctUntilChanged](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/distinctuntilchanged.html) | | |
| that occur too frequently | [throttle](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/throttle.html) | | |
| I want to compute | the sum | of its values | [sum](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/sum.html) |
| the average | [average](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/average.html) | | |
| using custom logic | and only output the final value | aggregate
reduce
| |
| and output the values as they are calculated | [scan](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/scan.html) | | |
| I want to wrap its messages with metadata | that describes each message | [materialize](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/materialize.html) | |
| that includes the time past since the last value | [timeInterval](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/timeinterval.html) | | |
| that includes a timestamp | [timestamp](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/timestamp.html) | | |
| after a period of inactivity | I want to throw an error | [timeout](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/timeout.html) | |
| I want to switch to another sequence | [timeout](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/timeout.html) | | |
| I want ensure there is only one value | and throw an error if there are more or less than one value | [single](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/single.html) | |
| and use the default value if there are no values | [singleOrDefault](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/singleordefault.html) | | |
| I want to only take the first value | and throw an error if there are no values | [first](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/first.html) | |
| and use the default value if there are no values | [firstOrDefault](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/firstordefault.html) | | |
| within a time period | [sample](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/sample.html) | | |
| I want to only take the last value | and error if there are no values | [last](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/last.html) | |
| and use the default value if there are no values | [lastOrDefault](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/lastordefault.html) | | |
| I want to know how many values it contains | [count](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/count.html) | | |
| I want to know if it includes a value | [contains](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/includes.html) | | |
| I want to know if a condition is satisfied | by any of its values | [any/some](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/any.html) | |
| by all of its values | [all/every](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/every.html) | | |
| I want to delay messages by a specific amount of time | | [delay](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/delay.html) | |
| based on custom logic | [delayWithSelector](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/delaywithselector.html) | | |
| I want to group the values | until the sequence completes | toArray
toMap
toSet
| |
| using custom logic | as arrays | [buffer](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/buffer.html) | |
| as sequences | [window](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/window.html) | | |
| in batches of a particular size | as arrays | [bufferWithCount](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/bufferwithcount.html) | |
| as sequences | [windowWithCount](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/windowwithcount.html) | | |
| based on time | as arrays | [bufferWithTime](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/bufferwithtime.html) | |
| as sequences | [windowWithTime](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/windowwithtime.html) | | |
| based on time or count, whichever happens first | as arrays | [bufferWithTimeOrCount](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/bufferwithtimeorcount.html) | |
| as sequences | [windowWithTimeOrCount](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/windowwithtimeorcount.html) | | |
| based on a key | until the sequence completes | [groupBy](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/groupby.html) | |
| and control the lifetime of each group | [groupByUntil](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/groupbyuntil.html) | | |
| I want to start a new sequence for each value | and emit the values from all sequences in parallel | [flatMap/selectMany](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/selectmany.html) | |
| and emit the values from each sequence in order | [concatMap/selectConcat](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/concatmap.html) | | |
| and cancel the previous sequence when a new value arrives | [flatMapLatest/selectSwitch](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/flatmaplatest.html) | | |
| and recursively start a new sequence for each new value | [expand](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/expand.html) | | |
| and emit values from all sequences depending for onNext, onError, and onCompleted in parallel | [flatMapObserver/selectManyObserver](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/flatmapobserver.html) | | |
| and emit values from all sequences depending for onNext, onError, and onCompleted in order | [concatMapObserver/selectConcatObserver](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/flatmapobserver.html) | | |
| I want to combine it with another | And be notified when both have completed | [forkJoin](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/forkjoin.html) | |
| I want to perform complex operations without breaking the fluent calls | [let](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/let.html) | | |
| I want to share a subscription between multiple subscribers | using a specific subject implementation | [multicast](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/multicast.html) | |
| | 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](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/retry.html) | |
| I want to start a new sequence | | [catch](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/catch.html) | |
| that depends on the error | [catch](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/catch.html) | | |
| when it completes | I want to re-subscribe | [repeat](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/repeat.html) | |
| I want to start a new sequence | [concat](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/concat.html) | | |
| when it completes or errors | I want to start a new sequence | [onErrorResumeNext](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/onerrorresumenext.html) | |
| when it completes, errors or unsubscribes | I want to execute a function | [finally](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/finally.html) | |
| I want to change the scheduler that routes | calls to subscribe | [subscribeOn](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/subscribeon.html) | |
| messages | [observeOn](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/observeon.html) | | |
| Using two sequences | I want to decide which to receive values from | based on which one has values first | [amb](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/amb.html) |
| I want to determine if their values are equal | [sequenceEqual](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/sequenceequal.html) | | |
| I want to combine their values | only when the first sequence emits, using the latest value from each | [withLatestFrom](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/withlatestfrom.html) | |
| in order | reusing the latest value when unchanged | [combineLatest](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/combinelatest.html) | |
| using each value only once | [zip](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/zip.html) | | |
| that share overlapping “lifetime” that I choose | and be notified for each combination | [join](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/join.html) | |
| and be given a sequence of “rights” for each “left” | [groupJoin](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/groupjoin.html) | | |
| I want to include values from both | [merge](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/observable/observable_instance_methods/merge.html) | | |
## See Also #\#
*Reference*
* [`Observable`](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/observable.md)
*Concepts*
* [Querying Observable Sequences](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/which_operator_do_i_use/querying.md)
* [Operators By Category](https://github.com/soufatn/rxjs-book/tree/bf8b6376d5d3357f915110c3a4f92267055843f3/content/which_operator_do_i_use/categories.md)