Recent questions tagged Scala

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scala - Joining two DataFrames in Spark SQL and selecting columns of only one

I have two DataFrames in Spark SQL (D1 and D2). I am trying to inner join both of them D1.join(D2, "some column ... this? I am using Spark 1.6. 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 - SBT including the version number in a program

I want a program I'm building to be able to report its own version at runtime (e.g. scala myprog.jar - ... defined in build.sbt at runtime? 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 - Why Future.sequence executes my futures in parallel rather than in series?

The word "sequence" means a series of actions one after the other. object Test { def main(args: Array[String]) ... (as opposed to in parallel) ? 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 - Unable to use for comprehension to map over List within Future

I have this issue that I have to work around every time. I can't map over something that is contained within a ... I'm using Scala 2.10.0. 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 - Noise free JSON format for sealed traits with Play 2.2 library

I need to get a simple JSON serialization solution with minimum ceremony. So I was quite happy finding this ... works out of the box. 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 - Checking if values in List is part of String

I have a string like this: val a = "some random test message" I have a list like this: val keys ... simply using standard library functions.) 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 this recursive List flattening work?

A while back this was asked and answered on the Scala mailing list: Kevin: Given some nested structure: List[List[. ... and does it have a name? See Question&Answers more detail:os...

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

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799 views

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scala - Context bounds shortcut with higher kinded-types

Is it possible to use the context bounds syntax shortcut with higher kinded-types? trait One { def test[W : ClassManifest] ... Unit } // hmm... 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 use an Akka Streams SourceQueue with PlayFramework

I would like to use a SourceQueue to push elements dynamically into an Akka Stream source. Play ... SourceQueue with PlayFramework? 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 - Best way to turn a Lists of Eithers into an Either of Lists?

I have some code like the below, where I have a list of Eithers, and I want to turn it into an Either of ... a more idiomatic way to do 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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668 views

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scala - What is the difference between unapply and unapplySeq?

Why does Scala have both unapply and unapplySeq? What is the difference between the two? When should I prefer one over the other? 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 - DataFrame equality in Apache Spark

Assume df1 and df2 are two DataFrames in Apache Spark, computed using two different mechanisms, e.g., Spark SQL ... a meaningful test data set. See Question&Answers more detail:os...

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

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786 views

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scala - Using .tupled method when companion object is in class

I am in the process of migrating from Slick to Slick 2, and in Slick 2 you are meant to use the tupled ... , so you can call tupled properly? See Question&Answers more detail:os...

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

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731 views

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scala - What is the best way to define custom methods on a DataFrame?

I need to define custom methods on DataFrame. What is the better way to do it? The solution should be scalable ... do it? Open 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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737 views

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scala - SLICK How to define bidirectional one-to-many relationship for use in case class

I am using SLICK 1.0.0-RC2. I have defined the following two tables Directorate and ServiceArea where ... table projection will 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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729 views

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scala - Joda DateTime Field on Play Framework 2.0's Anorm

I've been learning Play Framework, and the recommended way to access a database is using the build in anorm ... add a module for that? 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 - Why sbt runs dependency resolution every time after clean?

SBT runs dependency resolution every time after clean even if project dependency management configuration hasn't ... wrong or insufficient. See Question&Answers more detail:os...

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

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774 views

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scala - Recursive set union: how does it work really?

I am currently taking the Scala course on Coursera on my free time after work, in an attempt to finally give ... rather than how to code right. See Question&Answers more detail:os...

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

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801 views

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scala - How to check whether key or value exist in Map?

I have a scala Map and would like to test if a certain value exists in the map. myMap.exists( /*What should go here*/ ) See Question&Answers more detail:os...

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

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627 views

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scala - In Spark, what is the right way to have a static object on all workers?

I've been looking at the documentation for Spark and it mentions this: Spark's API relies heavily on ... serialize things would be appreciated. See Question&Answers more detail:os...

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

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607 views

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scala - Confused how to set up a multi-project sbt project

I'm using sbt .13 here. I have this so far: import sbt._ import Keys._ import play.Project._ object ... someone help me get this to 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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887 views

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scala - Filter Spark DataFrame by checking if value is in a list, with other criteria

As a simplified example, I tried to filter a Spark DataFrame with following code: val xdf = sqlContext.createDataFrame( ... using Spark 1.5.1 See Question&Answers more detail:os...

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

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772 views

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scala - Join two ordinary RDDs with/without Spark SQL

I need to join two ordinary RDDs on one/more columns. Logically this operation is equivalent to the database join ... How can this be 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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944 views

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scala - How do you update multiple columns using Slick Lifted Embedding?

How do you update multiple columns using Slick Lifted Embedding ? This document doesn't say much. I expected it to be ... .update("edit", "doc") See Question&Answers more detail:os...

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

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944 views

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scala - How to extract best parameters from a CrossValidatorModel

I want to find the parameters of ParamGridBuilder that make the best model in CrossValidator in Spark 1.4.x, In ... Any help? Thanks in advance, See Question&Answers more detail:os...

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

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729 views

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scala - How to perform one operation on each executor once in spark

I have a weka model stored in S3 which is of size around 400MB. Now, I have some set of record on which I ... records I don't load it again? See Question&Answers more detail:os...

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

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866 views

1 answer

scala - Pattern Matching `@` Symbol

Given this Person case class: scala> case class Person(name: String, age: Int) {} defined class Person ... ... missing the meaning/power of @? See Question&Answers more detail:os...

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

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759 views

1 answer

scala - How to deploy my spray API into production?

I'm thinking about how should be the process to deploy my already locally tested rest api to the cloud, ... apis to a production environment. See Question&Answers more detail:os...

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

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