Recent questions tagged Scala

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scala - "Unknown artifact. Not resolved or indexed" error for scalatest

I'm trying to modify the build.sbt file to add scalatest dependencies in IntelliJ IDEA. There's no error log ... is what my screen looks like: See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Converting nested case classes to nested Maps using Shapeless

I am trying to solve this question using Shapeless, in summary it's about converting a nested case class to ... the whole thing using Shapeless. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Returning original collection type in generic method

Say we want to make a function like minBy that returns all elements of equal minimalism in a collection: def ... the right collection type back? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Abstract types versus type parameters

In what situations should abstract types be preferred over type parameters? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - How to calculate the best numberOfPartitions for coalesce?

So, I understand that in general one should use coalesce() when: the number of partitions decreases due to a ... I would really appreciate it. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Difference between MutableList and ListBuffer

What is the difference between Scala's MutableList and ListBuffer classes in scala.collection.mutable? When would ... best structure for this? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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807 views

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scala - Merge maps by key

Say I have two maps: val a = Map(1 -> "one", 2 -> "two", 3 -> "three") val b = Map(1 -> ... there should be a nice, idiomatic way of doing this. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Can't prove that singleton types are singleton types while generating type class instance

Suppose I've got a type class that proves that all the types in a Shapeless coproduct are singleton ... enumerate the constructors manually? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Insert if not exists in Slick 3.0.0

I'm trying to insert if not exists, I found this post for 1.0.1, 2.0. I found snippet using ... yield ()).transactionally Thanks in advance See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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scala - Reading JSON with Apache Spark - `corrupt_record`

I have a json file, nodes that looks like this: [{"toid":"osgb4000000031043205","point":[508180.748,195333. ... is not corrupt and sound json. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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778 views

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scala class constructor parameters

What's the difference between: class Person(name: String, age: Int) { def say = "My name is " + name + ", age " + ... " + n + " birthday") n } } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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881 views

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scala - Reading DataFrame from partitioned parquet file

How to read partitioned parquet with condition as dataframe, this works fine, val dataframe = sqlContext.read.parquet(" ... data and it too big. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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679 views

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scala - Why is parameter in contravariant position?

I'm trying to use a covariant type parameter inside a trait to construct a case-class like so: trait MyTrait ... solution for this problem? Thx! See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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787 views

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scala - Filter spark DataFrame on string contains

I am using Spark 1.3.0 and Spark Avro 1.0.0. I am working from the example on the repository page. This following ... I do to do a "contains"? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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614 views

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scala - Why is Function[-A1,...,+B] not about allowing any supertypes as parameters?

I believe one can define covariance (at least, for objects) as 'the ability to use a value of a narrower ( ... Please advise where I'm mistaken. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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765 views

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scala - SBT stop run without exiting

How do you terminate a run in SBT without exiting? I'm trying CTRL+C but it exits SBT. Is there ... running application while keeping SBT open? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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787 views

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scala - Spark - Error "A master URL must be set in your configuration" when submitting an app

I have an Spark app which runs with no problem in local mode,but have some problems when submitting to the Spark ... ? Spark version: 1.6.1 See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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603 views

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scala - How to sort by column in descending order in Spark SQL?

I tried df.orderBy("col1").show(10) but it sorted in ascending order. df.sort("col1").show(10) also ... to use the native dataframe in spark. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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647 views

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scala - Why does join fail with "java.util.concurrent.TimeoutException: Futures timed out after [300 seconds]"?

I am using Spark 1.5. I have two dataframes of the form: scala> libriFirstTable50Plus3DF res1: org.apache.spark ... intensive? Can anyone help? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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528 views

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scala - Any vs underscore in generics

What is the different between the following Generics definitions in Scala: class Foo[T <: List[_]] and class Bar[T <: ... T <: List[_ <: Any]] See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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576 views

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scala - Easy idiomatic way to define Ordering for a simple case class

I have a list of simple scala case class instances and I want to print them in predictable, lexicographical order using ... lines,7) A(words,50) See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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457 views

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scala - Are HLists nothing more than a convoluted way of writing tuples?

I am really interested in finding out where the differences are, and more generally, to identify canonical use ... elements from component B. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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553 views

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scala - Is there a reason not to use SparkContext.getOrCreate when writing a spark job?

I'm writing Spark Jobs that talk to Cassandra in Datastax. Sometimes when working through a sequence of steps in ... when writing a spark job? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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654 views

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scala - Play: How to implement action composition

Given the followoing ActionBuilder implementations: class SignedRequest[A](request: Request[A]) extends WrappedRequest[A] ... something? Tx. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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712 views

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scala - Spark DataFrames when udf functions do not accept large enough input variables

I am preparing a DataFrame with an id and a vector of my features to be used later for doing predictions. I do a ... , or there is a better way? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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681 views

1 answer

scala - How to pattern match into an uppercase variable?

I have a method in Scala that returns a tuple, let's say the method is called 'test'. Then I ... directly into uppercase variables in Scala? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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626 views

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scala - Cake pattern with overriding abstract type don't work with Upper Type Bounds

I want to override abstract type in trait with <: and not with = (like answer here Scala Upper Bounds : value is ... not a member of S.this.T See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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902 views

1 answer

scala - Spark Row to JSON

I would like to create a JSON from a Spark v.1.6 (using scala) dataframe. I know that there is the ... definition. How can I achieve this? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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