Recent questions tagged scala

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scala - How to implement the SKI combinator calculus with match types?

I was trying to implement the SKI combinator calculus in Dotty using match types. A quick description of the SKI ... //Required: (K, K) 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 access objects within an object by mixing in a trait with reflection?

How can I get all of the objects within an object with reflection? Consider this code: object MonthDay extends ... (MonthDay) with reflection. 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 - In Spark Streaming, is there a way to detect when a batch has finished?

I use Spark 1.6.0 with Cloudera 5.8.3. I have a DStream object and plenty of transformations defined on ... allows me to achieve that? 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 - How to compare every element in the RDD with every other element in the RDD ?

I'm Trying to perform a K nearest neighbor search using spark. I have a RDD[Seq[Double]] and I'm planing ... with every other element in the RDD 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 - Is it possible to use json4s 3.2.11 with Spark 1.3.0?

Spark has a dependency on json4s 3.2.10, but this version has several bugs and I need to use 3.2.11. I added ... to force 3.2.11 version usage? 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 is the preferred way to avoid SQL injections in Spark-SQL (on Hive)

Assume a SchemaRDD rdd with a registered table customer. You want to filter out records according to ... .lang.StringEscapeUtils.escapeSql. 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 compute the inverse of a RowMatrix in Apache Spark?

I have a X, distributed matrix, in RowMatrix form. I am using Spark 1.3.0. I need to be able to calculate X inverse. 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 handle multi line rows in spark?

I am having a dataframe which has some multi-line observations: +--------------------+-------- ... doing any kind of transformation to the data? 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 - By-name repeated parameters

How to pass by-name repeated parameters in Scala? The following code fails to work: scala> def foo(s: (=> ... by name parameters to the method? 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 - "can't existentially abstract over parameterized type..."

I was messing around with Scala 2.8 for fun and trying to define a pimp which adds an "as" method to type ... and what the error message means. See Question&Answers more detail:os...

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

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879 views

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scala - Explicit return from play action

I have following action def login: Result = Action(parse.json) { request => if (/* Let's we say here ... else approach, code will be nightmare. See Question&Answers more detail:os...

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

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638 views

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scala - Iterating over an array in JSON with Play 2.1.1

I am using play 2.1.1 and I am having issues iterating through an array. I had read somewhere that you can ... = Json.reads[List[FBUser]] } 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 dependsOn usage - migration from 0.12 to 0.13

I have a command like this in build.sbt run <<= (run in Compile) dependsOn npmBuildTask According to documentation ... Could you please help me? 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 - Type safe method chaining that doesn't allow repeats of operations

I want to implement method chaining like in those questions: Best practice to implement Scala trait which supports ... 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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scala - Class type required but T found

I can't create an actor for some reason (here is a simple version of my class hierarchy): abstract class ... class type required but T found. See Question&Answers more detail:os...

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

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745 views

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scala - Difference between org.apache.spark.ml.classification and org.apache.spark.mllib.classification

I'm writing a spark application and would like to use algorithms in MLlib. In the API doc I found two different ... the reason for it? 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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860 views

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scala - Hash function in spark

I'm trying to add a column to a dataframe, which will contain hash of another column. I've found this piece ... I use a custom hash function? 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 - How to unwind array in DataFrame (from JSON)?

Each record in an RDD contains a json. I'm using SQLContext to create a DataFrame from the Json like this: ... Type: string (nullable = true) See Question&Answers more detail:os...

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

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758 views

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scala - Spark ML - Save OneVsRestModel

I am in the middle of refactoring my code to take advantage of DataFrames, Estimators, and Pipelines. I ... for making new predictions? 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 get application version in play framework and build.sbt

I'm using play 2.2 with Scala, how can I get version from build.sbt? name := "project_name" version : ... pass there value from another object? See Question&Answers more detail:os...

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

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728 views

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scala - Execute external command

I do not know whether it is a Scala or Play! question. I want to execute some external command from my ... Play version to serve the purpose? See Question&Answers more detail:os...

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

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962 views

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scala - Why is a `val` inside an `object` not automatically final?

What is the reason for vals not (?) being automatically final in singleton objects? E.g. object NonFinal { val ... , and thus also its members? See Question&Answers more detail:os...

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

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636 views

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scala - Standalone deployment of Scalatra servlet

I implemented a Scalatra servlet and now want to create an executable jar, just like described in this tutorial: http ... ) } 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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scala - Why use curly braces over parentheses?

In a lot of Scala examples I see people use curly braces in places I find outright strange, when the same ... of style and/or personal taste? See Question&Answers more detail:os...

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

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707 views

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scala - What's the performance impact of converting between `DataFrame`, `RDD` and back?

While my first instinct is to use DataFrames for everything, it's just not possible -- some operations are ... the scene in the conversion. See Question&Answers more detail:os...

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

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962 views

1 answer

scala - How to use Spark SQL DataFrame with flatMap?

I am using the Spark Scala API. I have a Spark SQL DataFrame (read from an Avro file) with the ... followed by groupBy using DataFrames? See Question&Answers more detail:os...

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

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709 views

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scala - Passing a Shapeless Extensible Record to a Function (continued)

Considering this question : Passing a Shapeless Extensible Record to a Function, Travis's answer shows that every ... way to progress? Benoit See Question&Answers more detail:os...

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

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1.2k views

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scala - Why is the error "Unable to find encoder for type stored in a Dataset" when encoding JSON using case classes?

I've written spark job: object SimpleApp { def main(args: Array[String]) { val conf = new SparkConf(). ... error. what is the problem? See Question&Answers more detail:os...

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

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