Kotlin Functional Programming

• Aggregation Operations
  • Sum
  • Max
• Transformations Operations
  • Zip
  • Flatten
  • Mapping

Aggregation Operations

Sum

• Get the total sum of numbers in a list

val listOfNumbers : List<Int> = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
val totalSum : Int = listOfNumbers.sum()

• Get the total sum of numbers in a range

val rangeOfNumbers : IntRange = 1..10
val totalSum : Int = rangeOfNumbers.sum()

• Get total sum of numbers in a list of Range

val listOfIntRange : List<IntRange> = listOf(1..10)
val totalSum : Int = listOfIntRange.sumBy(IntRange::sum)

Max

• Get the maximum value in the list of numbers

val listOfNumbers = listOf(100, 2, 43, 632, 55, 334)
val biggestValue = listOfNumbers.max()

• Get the maximum value in a list of number list

val listsOfNumbers = listOf(listOf(100, 2, 43), listOf(78, 565, 76), listOf(67, 443, 98))
val biggestValue = listsOfNumbers.flatten().max()

• Get the maximum value in a list of ranges list

val listsOfNumbers = listOf(listOf(1000..2000), listOf(1..10), listOf(200..300), listOf(5..7))

val biggestValue = listsOfNumbers
    .asSequence()
    .flatten()
    .flatten()
    .max()

Transformations Operations

• These functions build new collections from existing ones based on the transformation rules provided.

Zip

• Given the following data:

private val books = listOf(
    Book("harry potter"),
    Book("artemas the great")
)

private val authors = listOf(
    Author("joanne", "rowling"),
    Author("artemas", "prime")
)

• Zip to create a list of Pairs containing Books with Authors

val booksWithAuthors: List<Pair<Book, Author>> = books.zip(authors)

Flatten

val firstNumberSet = listOf(10, 20, 30)
val secondNumberSet = listOf(100, 90, 80)
val thirdNumberSet = listOf(40, 60, 50)

val numbers = listOf(firstNumberSet, secondNumberSet, thirdNumberSet)

• Get the total sum of all numbers

val sum = numbers.flatten().sum()

Mapping

• Given the following data:

val artemas = Author("artemas", "prime")
val kobe = Author("kobe", "bryant")
val james = Author("james", "harden")

val authors = listOf(artemas, kobe, james)

• Return a list of author names

val names = authors.map { it.name }

Association

• Given the following data:

val numbers = listOf("one", "two", "three", "four")

• Associate each word with it's length so that for example the input one will have an output one=3 where 3 is the length of the word.

val listOfNumbersAssociated = numbers.associateWith { it.length }