Recent questions tagged Scala

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scala - How to model an entity with many children in Sorm?

I have a Workspace and Document entities, with the idea that a workspace can contain zero, one, or more documents. My ... : Long, limit: Long) } 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 correctly type-annotate this HList?

sealed abstract trait HList case class :+:[H, T <: HList](head: H, tail: T) extends HList { def :+: ... fine when I remove the type annotation. 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 - Play slick and Async - is it a race condition?

Reading Play-Slick DBAction code, I thought that this code might contain a race condition: object DBAction{ // ... race condition in this 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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scala - Achieve concurrency when saving to a partitioned parquet file

When writing a dataframe to parquet using partitionBy : df.write.partitionBy("col1","col2","col3").parquet(path) It ... up to 750% of the cpus. 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 - Write/store dataframe in text file

I am trying to write dataframe to text file. If a file contains single column then I am able to write in ... Users/phadpa01/Desktop/op") } } 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 - Chaining operations on values without naming intermediate values

Sometimes I perform a sequence of computations gradually transforming some value, like: def complexComputation(input: ... is commonly done? 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 - Getting reference to a parameter of the outer function having a conflicting name

Please consider this code: trait A { def a : Int } def f ( a : Int ) = { def a0 = a new A ... function is not allowed as is changing the trait. 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 - spark kafka producer serializable

I come up with the exception: ERROR yarn.ApplicationMaster: User class threw exception: org.apache.spark.SparkException: ... . What I missed ? 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 run subprojects tests (including setup methods) sequentially when testing

EDIT4 Most of the text below the horizontal rule doesn't have anything to do with the real problem. ... called immediately for all subprojects. 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 - Read Kafka topic in a Spark batch job

I'm writing a Spark (v1.6.0) batch job which reads from a Kafka topic. For this I can use org. ... and stop streaming after the first batch? 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 - Most concise way to combine sequence elements

Say we have two sequences and we and we want to combine them using some method val a = Vector(1,2,3) val b = Vector ... val c = a zipmap b (_+_) 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 - Inferring type of generic implicit parameter from return type

Say I have a simple class like this abstract class Foo { implicit val impInt: Int = 42 def f[A]()(implicit a: ... [A] must be an Ordering[Int]? 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 - Kryo serialization refuses to register class

I'm trying to use kryo serialization with: kryo.setRegistrationRequired(true); I keep getting the following error saying ... Apache Spark v0.8.1 See Question&Answers more detail:os...

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

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scala - Creating a method definition tree from a method symbol and a body

Is there a convenient way to turn a MethodSymbol into the left-hand side of a method definition tree (i.e., ... this in the new Reflection API? See Question&Answers more detail:os...

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

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985 views

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scala - Weird behavior of & function in Set

Set is defined as Set[A]. It takes a in-variant parameter. Doing below works as expected as we are ... output for the same operation type. 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 - Error when Spark 2.2.0 standalone mode write Dataframe to local single-node Kafka

The data source is from Databricks Notebook demo:Five Spark SQL Helper Utility Functions to Extract and Explore Complex ... my command? 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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scala - Play framework handling session state

I have a Webapp that is built on top of the Play framework and Scala. It is about presenting the user ... would like to ask for suggestions. See Question&Answers more detail:os...

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

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927 views

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scala - Composing a list of all pairs

I'm brand new to Scala, having had very limited experience with functional programming through Haskell. I'd like ... have a good 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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936 views

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scala - Liftweb: create a form that can be submitted both traditionally and with AJAX

Is it possible in Lift web framework to create forms (and links) that react via AJAX, but also work without ... code, that would be best. 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 - Spark SQL filter multiple fields

What is the corrent syntax for filtering on multiple columns in the Scala API? If I want to do something like this: ... "group" !== "-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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scala - If case class inheritance is prohibited, how to represent this?

I am trying to create the case classes as explained in this article sealed abstract case class Exp() case class ... (x:Int) extends Exp ^ 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 - Turn Slick logging off

Slick fills up the console with a massive amount of log messages. I wanted, like the documentation suggested, ... - After phase insertCompiler: 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 compile single file in sbt

I'm doing some refactoring that made compiler temporally give errors in several files. I'd like to work ... that sbt functionality disclosure. 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 does curly braces following trait instantiation work?

I find some confusing use of trait in some unittesting code, such as: trait MyTrait { val t1 = ... // ... other cases might also be helpful? 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 find max in a list of tuples?

I have the following list of tuples: val arr = List(('a',10),('b',2),('c',3)) How to find the tuple ... or ('a', 10) for max value. See Question&Answers more detail:os...

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

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1.0k views

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scala - Inheriting a trait twice

This doesn't work: trait Trait class Class extends Trait with Trait Compiler complains: <console>:8: error: ... or pattern somehow useful? See Question&Answers more detail:os...

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

0 votes

1.1k views

1 answer

scala - Play framework handling session state

I have a Webapp that is built on top of the Play framework and Scala. It is about presenting the user ... would like to ask for suggestions. See Question&Answers more detail:os...

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

0 votes

1.1k views

1 answer

scala - Composing a list of all pairs

I'm brand new to Scala, having had very limited experience with functional programming through Haskell. I'd like ... have a good 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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