Recent questions tagged Scala

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scala - Write and read raw byte arrays in Spark - using Sequence File SequenceFile

How do you write RDD[Array[Byte]] to a file using Apache Spark and read it back 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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scala - Managing imports in Scalaz7

I am using scalaz7 in a project and sometimes I run into issues with imports. The simplest way get started is ... B] an instance of Applicative? 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 can't _ be used inside of string interpolation?

This works (x => s"$x") but this (s"${_}") results in [error] ...: unbound placeholder parameter [error ... string literal [error] (s"$_") 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 clone an iterator?

Suppose I have an iterator: val it = List("a","b","c").iterator I want a copy of it; my code is: val it2 ... . Is there any other API to do it? 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 make implicit Ordered on java.time.LocalDate

I want to use java.time.LocalDate and java.time.LocalDateTime with an implicit Ordered like: val date1 = ... <ChronoLocalDate>. Any idea? 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 - Replace groupByKey() with reduceByKey()

This is a follow up question from here. I am trying to implement k-means based on this implementation. It works ... RDD into a single sequence. 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 exact median for grouped data in Spark

I have a requirement to calculate exact median on grouped data set of Double datatype in Spark using Scala. It is different ... |0.25| +----+ 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 - Map from Class[T] to T without casting

I want to map from class tokens to instances along the lines of the following code: trait Instances { def put[T]( ... [T] instead of Class[T]? 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 - org.apache.spark.SparkException: Task not serializable

This is a working code example: JavaPairDStream<String, String> messages = KafkaUtils.createStream(javaStreamingContext, ... .scala:46) 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 - Companion class requires import of Companion object methods and nested objects?

I am looking at Akka related typesafe activator code and the following construct intrigued me: Companion object: ... import really is required. 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 the NotNull trait work in 2.8 and does anyone actually use it?

trait NotNull {} I've been trying to see how this trait can guarantee that something is not null and I can ... can find in programming 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 - Extract label values from a LabelledGeneric instance

Consider the following example: import shapeless._ case class Foo(bar: String, baz: Boolean) val labl = ... I can leverage it directly. 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 install a callback after request processing is finished in Spray?

I'm trying to serve large temporary files from Spray. I need to delete those files once HTTP request is complete. ... /logs can be updated, etc. 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 read parquet files using `ssc.fileStream()`? What are the types passed to `ssc.fileStream()`?

My understanding of Spark's fileStream() method is that it takes three types as parameters: Key, Value, and Format. ... feel free to share... 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 - Akka: actor current mailbox size or number of messages awaiting processing

I am trying to find out number of pending queue items which awaiting to be processed by the actor. I am sure ... system.mailboxes... size ?? } 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 a List into an Option if it is populated

I have a method that should convert a list to an Option of an object, or None if the list is empty. def ... more Scala-like 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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scala - DataFrame explode list of JSON objects

I have JSON data in the following format: { "date": 100 "userId": 1 "data": [ { "timeStamp": 101, ... I use a different approach all together? 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 - Adding a nested column to Spark DataFrame

How can I add or replace fields to a struct on any nested level? This input: val rdd = sc.parallelize(Seq( ... and apply the coalesce on each. 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 - Customer Type Mapper for Slick SQL

I've found this example from slick testing: https://github.com/slick/slick/blob/master/slick-testkit/src/ ... not finding/using the TypeMapper 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 the PartialFunction design inefficient?

This is something I've wondered about for a while. I see this pattern a lot: if (pf.isDefinedAt(in)) ... calling all of your extractors twice? 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 - Splitting string into groups

I'm trying to 'group' a string into segments, I guess this example would explain it more succintly scala> ... . Any help 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 - Map flatten and flatmap not equivalent

I thought that Scala construct map(f).flatten was equivalent to flatMap(f). But with this example, it is not the case. ... (1),2)) Any idea why? 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 - Does Spark maintain parquet partitioning on read?

I am having a lot trouble finding the answer to this question. Let's say I write a dataframe to parquet and ... answer would be helpful as well. 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 - Converting a tuple of options to an option of tuple with Scalaz or Shapeless

Having (Some(1), Some(2)) I expect to get Some((1, 2)) and having (Some(1), None) I expect to get 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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scala - What is the idiomatic way to pattern match sequence comprehensions?

val x = for(i <- 1 to 3) yield i x match { case 1 :: rest => ... // compile error } ... generalized Seq extractor part of the standard library? 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 - 1 :: List[Nothing] in foldLeft

If: scala> val l = List() // List() same as List[Nothing]() l: List[Nothing] = List() scala> 1 :: l res0: List[ ... acc x -> x:acc) [] [1,2,3] 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 - Insert a new element in a specified position of a list

There is no built-in function or a method of a List that would allow user to add a new element in a certain position of ... List(1, 2, 3, 4, 5) See Question&Answers more detail:os...

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

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1.6k views

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scala - Map[String,Any] to compact json string using json4s

I am currently extracting some metrics from different data sources and storing them in a map of type Map[String, ... what I want to accomplish? See Question&Answers more detail:os...

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

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