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![Lets begin the collection
Lists
scala> val Numbers = List(1, 2, 3, 4)
numbers: List[Int] = List(1, 2, 3, 4)
Numbers :+= 5 //error of reassignment
Numbers ++= List(6,7,8) //error of reassignment
Numbers ++= List(9,”Harsh”)//type mismatch](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-7-2048.jpg)
![Lets begin the collection
Sets
Sets have no duplicates
scala> var Numbers = Set(1, 1, 2)
res0: scala.collection.immutable.Set[Int] = Set(1, 2)
Numbers += “Knoldus” // type mismatch error
Numbers += 2 // blank or no output having 1 and 2 as elements
Numbers += 3 //scala.collection.immutable.Set[Int] =
Set(1, 2, 3)](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-8-2048.jpg)
![Lets begin the collection
Option[T] is used when the method might not return what we ask
for
● scala> val numbers = Map("one" -> 1, "two" -> 2)
numbers: scala.collection.immutable.Map[java.lang.String,Int] =
Map(one -> 1, two -> 2)
● scala> numbers.get("two")
res0: Option[Int] = Some(2)
● scala> numbers.get("three")
res1: Option[Int] = None](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-14-2048.jpg)
![Functional combinators
map: evaluates a function over each element of list
scala> val numbers=List(1,2,3,4)
numbers: List[Int] = List(1, 2, 3, 4)
scala> numbers.map((i: Int) => i * 2)
res1: List[Int] = List(2, 4, 6, 8)
foreach: A kind of map but returns nothing
scala> val doubled = numbers.foreach((i: Int) => i * 2)
doubled: Unit = ()](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-15-2048.jpg)
![Functional combinators
filter: removes elements when function we pass evaluates to
false
scala> numbers.filter((i: Int) => i % 2 == 0)
res0: List[Int] = List(2, 4)
zip: Zips contents of multiple lists into one single list
scala> List(1, 2, 3).zip(List("a", "b", "c"))
res0: List[(Int, String)] = List((1,a), (2,b), (3,c))](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-16-2048.jpg)
![Functional combinators
partition: splits a list based on where it falls with respect to a
predicate function.
scala> val numbers = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> numbers.partition(_ % 2 == 0)
res0: (List[Int], List[Int]) = (List(2, 4, 6, 8, 10),List(1, 3, 5, 7, 9))
find: returns the first element of a collection that matches a
function.
scala> numbers.find((i: Int) => i > 5)
res0: Option[Int] = Some(6)](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-17-2048.jpg)
![Functional combinators
drop: drops the first i elements
scala> numbers.drop(5)
res0: List[Int] = List(6, 7, 8, 9, 10)
● dropWhile: removes the first elements that match a predicate
function
scala> numbers.dropWhile(_ % 2 != 0)
res0: List[Int] = List(2, 3, 4, 5, 6, 7, 8, 9, 10)](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-18-2048.jpg)
![Functional combinators
flatten: collapses nested structures
–
– scala> List(List(1, 2), List(3, 4)).flatten
– res0: List[Int] = List(1, 2, 3, 4)](https://image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-22-2048.jpg)
![Lets begin the collection
Lists
scala> val Numbers = List(1, 2, 3, 4)
numbers: List[Int] = List(1, 2, 3, 4)
Numbers :+= 5 //error of reassignment
Numbers ++= List(6,7,8) //error of reassignment
Numbers ++= List(9,”Harsh”)//type mismatch](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-7-2048.jpg)
![Lets begin the collection
Sets
Sets have no duplicates
scala> var Numbers = Set(1, 1, 2)
res0: scala.collection.immutable.Set[Int] = Set(1, 2)
Numbers += “Knoldus” // type mismatch error
Numbers += 2 // blank or no output having 1 and 2 as elements
Numbers += 3 //scala.collection.immutable.Set[Int] =
Set(1, 2, 3)](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-8-2048.jpg)
![Lets begin the collection
Option[T] is used when the method might not return what we ask
for
● scala> val numbers = Map("one" -> 1, "two" -> 2)
numbers: scala.collection.immutable.Map[java.lang.String,Int] =
Map(one -> 1, two -> 2)
● scala> numbers.get("two")
res0: Option[Int] = Some(2)
● scala> numbers.get("three")
res1: Option[Int] = None](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-14-2048.jpg)
![Functional combinators
map: evaluates a function over each element of list
scala> val numbers=List(1,2,3,4)
numbers: List[Int] = List(1, 2, 3, 4)
scala> numbers.map((i: Int) => i * 2)
res1: List[Int] = List(2, 4, 6, 8)
foreach: A kind of map but returns nothing
scala> val doubled = numbers.foreach((i: Int) => i * 2)
doubled: Unit = ()](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-15-2048.jpg)
![Functional combinators
filter: removes elements when function we pass evaluates to
false
scala> numbers.filter((i: Int) => i % 2 == 0)
res0: List[Int] = List(2, 4)
zip: Zips contents of multiple lists into one single list
scala> List(1, 2, 3).zip(List("a", "b", "c"))
res0: List[(Int, String)] = List((1,a), (2,b), (3,c))](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-16-2048.jpg)
![Functional combinators
partition: splits a list based on where it falls with respect to a
predicate function.
scala> val numbers = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> numbers.partition(_ % 2 == 0)
res0: (List[Int], List[Int]) = (List(2, 4, 6, 8, 10),List(1, 3, 5, 7, 9))
find: returns the first element of a collection that matches a
function.
scala> numbers.find((i: Int) => i > 5)
res0: Option[Int] = Some(6)](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-17-2048.jpg)
![Functional combinators
drop: drops the first i elements
scala> numbers.drop(5)
res0: List[Int] = List(6, 7, 8, 9, 10)
● dropWhile: removes the first elements that match a predicate
function
scala> numbers.dropWhile(_ % 2 != 0)
res0: List[Int] = List(2, 3, 4, 5, 6, 7, 8, 9, 10)](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-18-2048.jpg)
![Functional combinators
flatten: collapses nested structures
–
– scala> List(List(1, 2), List(3, 4)).flatten
– res0: List[Int] = List(1, 2, 3, 4)](https://crownmelresort.com/image.slidesharecdn.com/harshknolxsessiononscalacollections-150213005637-conversion-gate01/75/Collections-In-Scala-22-2048.jpg)
Uploaded byKnoldus Inc.
Collections In Scala
This document discusses Scala collections. It provides an introduction to Scala collections and code examples of using various collection types like lists, sets, tuples, maps, and options. It also covers functional combinators that can be used on collections, such as map, filter, foldLeft, and flatten.
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Collections In Scala
- 1. Collections In Scala Collections In Scala Harsh Sharma Software Consultant- Trainee Knoldus Software LLP Harsh Sharma Software Consultant - Trainee Knoldus Software LLP
- 2. AgendaAgenda ● Why Collections?I love collections ● Introduction to Scala collections ● Code examples ● Why Collections? I love collections ● Introduction to Scala collections ● Code examples
- 3. Why collections?Why collections? Nocomplicated looping structures and recursions Side-effect-free operations No interference between iterators and collections No complicated looping structures and recursions Side-effect-free operations No interference between iterators and collections
- 4.
- 5. I love collections– Why?
- 6.
- 7. Lets begin thecollection Lists scala> val Numbers = List(1, 2, 3, 4) numbers: List[Int] = List(1, 2, 3, 4) Numbers :+= 5 //error of reassignment Numbers ++= List(6,7,8) //error of reassignment Numbers ++= List(9,”Harsh”)//type mismatch
- 8. Lets begin thecollection Sets Sets have no duplicates scala> var Numbers = Set(1, 1, 2) res0: scala.collection.immutable.Set[Int] = Set(1, 2) Numbers += “Knoldus” // type mismatch error Numbers += 2 // blank or no output having 1 and 2 as elements Numbers += 3 //scala.collection.immutable.Set[Int] = Set(1, 2, 3)
- 9. Lets begin thecollection Tuple A tuple groups together simple logical collections of items without using a class. scala> val hostPort = ("localhost", 80) hostPort: (String, Int) = (localhost, 80)
- 10. Lets begin thecollection Tuples do not have named accessors, like case classes Just have their position as 1-based Have limit of 22 elements scala> hostPort._1 res0: String = localhost scala> hostPort._2 res1: Int = 80
- 11. Lets begin thecollection Tuples satisfies the pattern matching nicely hostPort match { case ("localhost", port) => ... case (host, port) => ... }
- 12. Lets begin thecollection Special sauce to create tuple of two elements scala> 1 -> 2 res0: (Int, Int) = (1,2) scala> "Harsh"->"Sharma"->"Khandal" res4: ((String, String), String) = ((Harsh,Sharma),Khandal)
- 13. Lets begin thecollection ● Map can hold basic datatypes ● Collection of tuples ● Can contain maps and functions as values ● Map(1 -> 2) Map("foo" -> "bar") ● Map(1 -> Map("foo" -> "bar")) ● Map("timesTwo" -> { timesTwo(_) })
- 14. Lets begin thecollection Option[T] is used when the method might not return what we ask for ● scala> val numbers = Map("one" -> 1, "two" -> 2) numbers: scala.collection.immutable.Map[java.lang.String,Int] = Map(one -> 1, two -> 2) ● scala> numbers.get("two") res0: Option[Int] = Some(2) ● scala> numbers.get("three") res1: Option[Int] = None
- 15. Functional combinators map: evaluatesa function over each element of list scala> val numbers=List(1,2,3,4) numbers: List[Int] = List(1, 2, 3, 4) scala> numbers.map((i: Int) => i * 2) res1: List[Int] = List(2, 4, 6, 8) foreach: A kind of map but returns nothing scala> val doubled = numbers.foreach((i: Int) => i * 2) doubled: Unit = ()
- 16. Functional combinators filter: removeselements when function we pass evaluates to false scala> numbers.filter((i: Int) => i % 2 == 0) res0: List[Int] = List(2, 4) zip: Zips contents of multiple lists into one single list scala> List(1, 2, 3).zip(List("a", "b", "c")) res0: List[(Int, String)] = List((1,a), (2,b), (3,c))
- 17. Functional combinators partition: splitsa list based on where it falls with respect to a predicate function. scala> val numbers = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) scala> numbers.partition(_ % 2 == 0) res0: (List[Int], List[Int]) = (List(2, 4, 6, 8, 10),List(1, 3, 5, 7, 9)) find: returns the first element of a collection that matches a function. scala> numbers.find((i: Int) => i > 5) res0: Option[Int] = Some(6)
- 18. Functional combinators drop: dropsthe first i elements scala> numbers.drop(5) res0: List[Int] = List(6, 7, 8, 9, 10) ● dropWhile: removes the first elements that match a predicate function scala> numbers.dropWhile(_ % 2 != 0) res0: List[Int] = List(2, 3, 4, 5, 6, 7, 8, 9, 10)
- 19. Functional combinators foldLeft: valuepassed as argument is the initial value and m is the accumulator scala> numbers.foldLeft(0)((m: Int, n: Int) => m + n) res0: Int = 55 – scala> numbers.foldLeft(0) { (m: Int, n: Int) => println("m: " + m + " n: " + n); m + n }
- 20. Functional combinators scala> numbers.foldLeft(0){ (m: Int, n: Int) => println("m: " + m + " n: " + n); m + n } m: 0 n: 1 m: 1 n: 2 m: 3 n: 3 m: 6 n: 4 m: 10 n: 5 m: 15 n: 6 m: 21 n: 7 m: 28 n: 8 m: 36 n: 9 m: 45 n: 10 res0: Int = 55
- 21. Functional combinators foldRight: Assame as foldLeft, but performs from opposite direction scala> numbers.foldRight(0) { (m: Int, n: Int) => println("m: " + m + " n: " + n); m + n } m: 10 n: 0 m: 9 n: 10 m: 8 n: 19 m: 7 n: 27 m: 6 n: 34 m: 5 n: 40 m: 4 n: 45 m: 3 n: 49 m: 2 n: 52 m: 1 n: 54 res0: Int = 55
- 22. Functional combinators flatten: collapsesnested structures – – scala> List(List(1, 2), List(3, 4)).flatten – res0: List[Int] = List(1, 2, 3, 4)