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Questions tagged [flatmap]

flatMap is a Java and Scala function that works by applying a function that returns a sequence for each element in the list, and flattening the results into the original list.

flatMap works by applying a function that returns a sequence for each element in the list, and flattening the results into the original list. This is easier to show than to explain:

scala> def g(v:Int) = List(v-1, v, v+1)
g: (v: Int)List[Int]

scala> l.map(x => g(x))
res64: List[List[Int]] = List(List(0, 1, 2), List(1, 2, 3), List(2, 3, 4), List(3, 4, 5), List(4, 5, 6))

scala> l.flatMap(x => g(x))
res65: List[Int] = List(0, 1, 2, 1, 2, 3, 2, 3, 4, 3, 4, 5, 4, 5, 6)

Source: http://www.brunton-spall.co.uk/post/2011/12/02/map-map-and-flatmap-in-scala/

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spark rdd how to flat Key - Array(value) pair

I have a park paired rdd (key, Array(value1, value2, value3.....)). what scala statement should I wrote? How could I flat this rdd and creating a new rdd : (key, value1), (key, value2), (key, value3)....
sickcat
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Why is the flatmap-operator not working as I understood it?

fetch(url) returns a promise, which I'm converting to observable using flatmap. Why is this not working? Rx.Observable .from(imgSrc) .map(url => fetch(url)) .flatmap( res => R.Observable.fromPromise(res)) .subscribe( …
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Returning value from a Scala Future

In the below code, I'm trying to do two operations. One, to create a customer in a db, and the other, to create an event in the db. The creation of the event, is dependent on the creation of the user. I'm new to Scala, and confused on the role of…
Rafa
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How can I chain a subscription to a url parameter to a subscription in a service?

I am trying to create a component that subscribes to the id url parameter in the activated route, and then uses it to call a service of mine that makes an http request to a server with the id. I have a route that takes in an id like so -…
LayfieldK
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Filter data from a filtered array

I'm just beginning to understand the use of flatMap, etc. To make filters to my arrays. The problem is that I don't understand well how to make filters within others to make my search more efficient, specifically I need to extract the elements of…
Diego Salinas Flores
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Unsupported Exception while modifying list inside flatmap function

I get an Unsupported Operation Exception when trying to modify a list from inside "apply" method of flatmap in RxJava2. compositeDisposable.add(createObservable() .flatMap(new Function, ObservableSource>>() { …
Gaurav
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JSON and flatMap - error Computed property must have an explicit type

I am having a difficulty with flatMap on returned json data. How can I Implement flatMap in the following code. I keep receiving an error: Computed property must have an explicit type let task = URLSession.shared.dataTask(with: request) { data,…
Luke
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Why flatMap is implemented with merge in RxJava?

Why is RxJava 1.x flatMap() operator is implemented with merge? public final Observable flatMap(Func1> func) { if (getClass() == ScalarSynchronousObservable.class) { return…
Kurovsky
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Scala - How to convert Map[Int,List[List[IntVar]]] to

I am new in Scala programming and the flatmap function gives me headache. Before you ask me to search, I made some research on Stackoverflow : https://stackoverflow.com/search?q=scala+map+to+list but I didn't find something to solve easily my…
jy95
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Reverse a word-frequency map in Scala

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Darth.Vader
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How to open an Option[Map(A,B)] in Scala?

I've done enough Scala to know what ugly code looks like. Observe: val sm Option[Map[String,String]] = Some(Map("Foo" -> "won", "Bar" -> "too", "Baz" -> "tree")) Expected output: : String = Foo=won,Bar=too,Baz=tree Here's my Tyler Perry code…
dlite922
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Immutable.js and flatMap equivalent function

Was just wondering if there an equivalent flatMap function in Immutable.js? I have been using this node package https://www.npmjs.com/package/flatmap for a while but I would prefer to write things like this listObject.flatMap(x => ...) Instead…
foomip
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How to express the following nested futures with for-comprehension

My question: is it possible to simplify this nested expression with for-comprehension ? run(dbAction).flatMap(insertedJobs => { Future.sequence(insertedJobs.map { job => recordingBean.findStreamsForInterval(job.mediaSource, job.begin,…
Slow Harry
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I have a Spark RDD of type (Array[breeze.linalg.DenseVector[Double]], breeze.linalg.DenseVector[Double]). I wish to flatten its key to transform it into a RDD of type breeze.linalg.DenseVector[Double], breeze.linalg.DenseVector[Double]). I am…
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