https://github.com/rtyley/scala-collection-plus

a few extras to handle Scala 2.13's deprecation of `.mapValues()`
https://github.com/rtyley/scala-collection-plus

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a few extras to handle Scala 2.13's deprecation of `.mapValues()`

• Host: GitHub
• URL: https://github.com/rtyley/scala-collection-plus
• Owner: rtyley
• Created: 2019-12-28T13:01:55.000Z (almost 5 years ago)
• Default Branch: master
• Last Pushed: 2022-07-12T11:42:39.000Z (over 2 years ago)
• Last Synced: 2024-05-01T23:01:48.800Z (6 months ago)
• Topics: scala
• Language: Scala
• Size: 37.1 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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# scala-collection-plus

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A few extras to handle Scala 2.13's deprecation of `.mapValues()`

I'm just a developer, standing in front of a Scala v2.13 `Map`, asking it to map its values.

```scala

import com.madgag.scala.collection.decorators._

```

## `mapV`

A concise replacement for `mapValues()`, that generates immutable Maps and

avoids the verbose `.view.mapValues(f).toMap` syntax that becomes necessary

in Scala 2.13:

```scala

val m = Map("foo" -> 5, "bar" -> 10)

// m: Map[String, Int] = Map("foo" -> 5, "bar" -> 10)

def f(i: Int) = i + 1

m.transform{case(_,v)=>f(v)}

// res0: Map[String, Int] = Map("foo" -> 6, "bar" -> 11)

m.view.mapValues(f).toMap

// res1: Map[String, Int] = Map("foo" -> 6, "bar" -> 11)

m.mapValues(f)

// res2: collection.MapView[String, Int] = MapView(("foo", 6), ("bar", 11))

m.mapV(f)                    

// res3: Map[String, Int] = Map("foo" -> 6, "bar" -> 11)

```

## `groupUp`

Scala 2.13 introduced 

[`groupMap` & `groupMapReduce`](https://docs.scala-lang.org/overviews/core/collections-migration-213.html#are-there-new-operations-on-collections)

(see original GitHub [Issue](https://github.com/scala/collection-strawman/issues/42) &

[PR](https://github.com/scala/collection-strawman/pull/253)) which potentially are another

way to avoid the verbosity of `mapValues` in Scala 2.13. In the codebase I'm working on, there

were unfortunately only a few examples where they were applicable.

 

There were more than twice as many opportunities to use a new `groupUp(k)(g)` method,

equivalent to `s.groupBy(k).view.mapValues(g).toMap` - the difference is that while

`groupMap` requires you to `map` over the individual elements in each collection that

forms a value in the `Map`, `groupUp` instead allows you to perform _any_ operation

(not just `map`) that you might want. In the codebase I'm working on, that turns out

to be more useful.

```scala

val s = Seq("foo", "foo", "bar", "bang")

// s: Seq[String] = List("foo", "foo", "bar", "bang")

def k(str: String) = str.length

def g(strs: Seq[String]) = strs.size

s.groupBy(k).view.mapValues(g).toMap // Scala 2.13 syntax

// res4: Map[Int, Int] = Map(3 -> 3, 4 -> 1) // Scala 2.13 syntax

s.groupBy(k).mapValues(g)            // deprecated in Scala 2.13, now returns MapView[K,B]

// res5: collection.MapView[Int, Int] = MapView((3, 3), (4, 1))            // deprecated in Scala 2.13, now returns MapView[K,B]

s.groupUp(k)(g)                      // provided by scala-213-collections-plus

// res6: Map[Int, Int] = Map(3 -> 3, 4 -> 1)

```