Recent questions tagged scala

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scala - Impredicative types vs. plain old subtyping

A friend of mine posed a seemingly innocuous Scala language question last week that I didn't have a good answer ... example above) in Scala? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - How to filter None's out of List[Option]?

If I have a List[Option[A]] in Scala, what is the idiomatic way to filter out the None values? One way ... way? This does seem pretty simple. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Create new column with function in Spark Dataframe

I'm trying to figure out the new dataframe API in Spark. seems like a good step forward but having trouble ... withColumn? Thanks for your help. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Create Simple Project SBT 0.10.X

(This is a follow up to sbt not creating projects correctly. The question wasn't answered.) Basically, that question ... under sbt 0.10.X? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Convert List of tuple to map (and deal with duplicate key ?)

I was thinking about a nice way to convert a List of tuple with duplicate key [("a","b"),("c","d"),("a" ... turn into a map of (Int -> NodeSeq) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Extract column values of Dataframe as List in Apache Spark

I want to convert a string column of a data frame to a list. What I can find from the Dataframe API ... would be appreciated. Thank you! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - What does "coalgebra" mean in the context of programming?

I have heard the term "coalgebras" several times in functional programming and PLT circles, especially when the ... to objects and comonads? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - How to get Kafka messages based on timestamp

I am working on a application in which I am using kafka and tech is scala. My kafka consumer code is as follows ... Any way I can achieve this? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Have a List in Play framework web service parameters

I have written this web service in play framework. controller def getByGenre(genre: String) = Action { val ... the web service using CURL. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Turning Map("a" -> 2, "b" -> 1) into seq("a","a","b") using map

I am trying to turn a Map("a" -> 2, "b" -> 1) into seq("a","a","b") through the map function, ... (x)) multiset = multiset :+ variables(x) } See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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742 views

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scala - toList on Range with suffix notation causes type mismatch

I am just starting with Scala, and trying out some things on Range and List, I get something very strange with a ... . Scala version is 2.9.2 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - NullPointerException on implicit resolution

This code results in NullPointerException: import anotherpackage.MyContext import anotherpackage.builders.aMyContext case ... field itself? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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671 views

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scala - Spark Fixed Width File Import Large number of columns causing high Execution time

I am getting the fixed width .txt source file from which I need to extract the 20K columns. As lack of libraries ... can I tune this Job or code See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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828 views

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scala - muliline string split

I have this: val msg = "Preparado para cocinar..." val message = msg.splitAt(msg.length()/2) println(message ... in the middle of the sentence? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Defining `Reads` for JSON Set Type

How can I create a play.api.libs.Reads for my People case class? scala> type Id = Long defined type alias Id scala ... ").read[Set[Id]])(People) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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822 views

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scala - remove NULL columns in Spark SQL

How to remove columns containing only null values from a table? Suppose I have a table - SnapshotDate CreationDate ... using spark 1.6.1 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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825 views

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scala - Slick 3.0-RC3 fails with java.util.concurrent.RejectedExecutionException

I'm trying to get familiar with Slick 3.0 and Futures (using Scala 2.11.6). I use simple code based ... .reflect.Method.invoke(Method.java:606) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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673 views

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scala - How to use update output mode with FileFormat format?

I am trying to use spark structured streaming in update output mode write to a file. I found this ... match that ensures Append Mode. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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693 views

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scala - How to access local files in Spark on Windows?

I am using Spark on Windows. I know in *nix, accessing local file code likes this: val textFile = sc.textFile("file ... .md" But all can't work. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - XML insert/update

do you know any Scala API to insert and (or) update Nodes according to XPath? e.g for a given Node and ... copy of XML with new node thanks See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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727 views

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scala - Inheritance and code reuse in stackable traits

In this simplified experiment, I want to be able to quickly build a class with stackable traits that can ... specified in it's implementation? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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760 views

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scala - How to get the TypeTag for a class in Java

I'm trying to call the functions.typedLit from Spark library in my other question. And it asks for two parameters, ... >>typedLit(seq, ???) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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780 views

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scala - Combining 2 Options into 1

Is there a predefined function x in Scala that combine 2 Options so that Some(a) x None => Some(a) None x Some(b) => Some(b) None x None => None See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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645 views

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scala - When doing implicit resolution with type parameters, why does val placement matter?

In one file, I have: trait JsonSchema[T] { val propertyType: String override def toString: String = ... compatibility still be maintained? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Slick 3 reusable generic repository

I am experiencing issues making Slick's TableQuery used in a generic fashion. Observe the regular situation: class ... idea about the solution? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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826 views

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scala - Implicit view not working - is my implicit def to blame?

I'm having some trouble with an implicit view. I suspect this is quite trivial and may have some ... ? Any help gratefully received. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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683 views

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scala - Why is there a difference in behavior between these two pattern matches in a for comprehension?

Consider this Map[String, Any]: val m1 = Map(("k1" -> "v1"), ("k2" -> 10)) Now let's ... the second scenario without using a dirty isInstanceOf? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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807 views

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scala - Play - How to use different configuration files for Dev/Prod?

I have a project with the following configuration Commons.conf Application.conf for development Production.conf for ... the production ones? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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