A group method on TraversableOnce (and subclasses) that relies on the element order and preserves it.

import com.agilogy.utils.Groupable._
val people: Seq[Person] = ???
val peopleByName:Seq[(Name,Seq[Person])] = people.group(by = _.name)

It behaves somewhat like the standard groupBy but:

• It relies on the order of the traversable creating a group for each consecutive element that returns the same group key
• It preserves the order of the returned groups
• It returns a Seq of pairs key -> Seq(value) instead of a Map.
  • I could have used a ListMap, but the seq makes it evident that lookup time is linear.

The method is added to TraversableOnce and subclasses via Pimp my Library Pattern.

resolvers += "Agilogy GitLab" at "https://gitlab.com/api/v4/groups/583742/-/packages/maven"

libraryDependencies += "com.agilogy" %% "groupable" % "1.2"

Import Groupable._:

import com.agilogy.utils.Groupable._

Now, two new methods group are available on TraversableOnce[T]:

def group[GT, RT](by: ((T) => GT)): Seq[(GT, Seq[T])]
def group[GT, RT](by: (T) ⇒ GT, as: (T) ⇒ RT): Seq[(GT, Seq[RT])]

Example (from the tests):

it should "group mapping values" in {
  val s = Seq("email" -> "j@example.com", "email" -> "k@example.com", "name" -> "John")
  val res = s.group(by = _._1, as = _._2)
  assert(res === Seq("email" -> Seq("j@example.com", "k@example.com"), "name" -> Seq("John")))
}

• Maybe we could use a typeclass so that not only TraversableOnes are groupables. As an example, it could be interesting for ResultSets.

To publish this package to Agilogy's Package Registry, set the GITLAB_DEPLOY_TOKEN environment variable and then run the following command in sbt:

sbt:groupable> +publish

Copyright 2015 Agilogy

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

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