Scala Higher Order Functions

Practical ScalaHOF

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Scala, Java, Objective-C

1. HOF Higher Order FunctionsA function that takes a function as argument

or returns another functione.g. map & filter

map transforms data

map sadness to happiness

:( :( :( => :) :) :)

map sadness to happiness - JAVA

public List<String> mapSadnessToHappiness (List<String> sadness) {

List<String> happiness = new ArrayList<String>(sadness.size()); for (int i = 0; i < sadness.size(); i++) { String sadFace = sadness.get(i); String happyFace = sadFace.replace('(', ')'); happiness.add(happyFace); } return happiness;

} List<String> sadness = Arrays.asList(":(", ":(", ":("); List<String> happiness = mapSadnessToHappiness(sadness);

map sadness to happiness - Scala

List(":(", ":(", ":(").map(face => face.replace('(', ')'))

map sadness to happiness - Scala

List(":(", ":(", ":(").map(_.replace('(', ')'))

filter remove the unwanted

filter sadness keeping happiness

:) :) :( => :) :)

filter sadness keeping happiness

List(":)", ":)", ":(").filter(_.contains(":)"))

Idiomatic TransformationsCount char occurrences on a String - JAVA

public static int countCharOccurrences(String haystack, char needle) { int count = 0; for (int i = 0; i < haystack.length(); i++) { if (haystack.charAt(i) == needle) { count++; } } return count; }

public static Map<Character, Integer> toCharOccurrenceMap(String haystack) { Map<Character, Integer> map = new HashMap<Character, Integer>(); if (haystack != null) { for (int i = 0; i < haystack.length(); i++) { char character = haystack.charAt(i); int count = countCharOccurrences(haystack, character); map.put(character, count); } } return map; }

toCharOccurrenceMap("betabeers");

Idiomatic TransformationsCount char occurrences on a String

"betabeers" groupBy identity mapValues (_.size)

Key differentiatorHigher Order Functions help with most Collection problems that you usually solve by looping over and manually creating

intermediate containers. Transformed results stay immutable and thread safe.

No need to reinvent the wheel.Code becomes readable and idiomatic

"betabeers" groupBy identity mapValues (_.size)

Other Powerful HOF’s examples

Sum(1 to 1000).reduceLeft( _ + _ )

(1 to 1000).sum

Partition filterval (passed, failed) = List(49, 58, 88, 90) partition ( _ > 60 )

minList(14, 35, -7, 46, 98).min

maxList(14, 35, -7, 46, 98).max

Imperative iteration(1 to 10) foreach (println)

Parallel Collections(1 to 10).par foreach(_ => println(Thread.currentThread.getName))

Become a Scala Master

For comprehensionsCase Classes

FuturesOptionsTraitsEither

Pattern MatchingMonadsActorsDSL’s

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