Appending an element to the end of a list in Scala

Question

I can t add an element of type T into a list List T   I tried with myList     myElement but it seems it creates a strange object and accessing to myList last always returns the first element that was put inside the list  How can I solve this problem

User · Answer

Lists in Scala are not designed to be modified. In fact, you can't add elements to a Scala List; it's an immutable data structure, like a Java String. What you actually do when you "add an element to a list" in Scala is to create a new List from an existing List. (Source)

Instead of using lists for such use cases, I suggest to either use an ArrayBuffer or a ListBuffer. Those datastructures are designed to have new elements added.

Finally, after all your operations are done, the buffer then can be converted into a list. See the following REPL example:

scala> import scala.collection.mutable.ListBuffer
import scala.collection.mutable.ListBuffer

scala> var fruits = new ListBuffer[String]()
fruits: scala.collection.mutable.ListBuffer[String] = ListBuffer()

scala> fruits += "Apple"
res0: scala.collection.mutable.ListBuffer[String] = ListBuffer(Apple)

scala> fruits += "Banana"
res1: scala.collection.mutable.ListBuffer[String] = ListBuffer(Apple, Banana)

scala> fruits += "Orange"
res2: scala.collection.mutable.ListBuffer[String] = ListBuffer(Apple, Banana, Orange)

scala> val fruitsList = fruits.toList
fruitsList: List[String] = List(Apple, Banana, Orange)

User · Answer

List 1 2 3     4  Results in List Int    List 1  2  3  4    Note that this operation has a complexity of O n   If you need this operation frequently  or for long lists  consider using another data type  e g  a ListBuffer

User · Answer

We can append or prepend two lists or list amp array Append  var l   List 1 2 3      l   l    4  Result   1 2 3 4   var ar   Array 4  5  6      for x  lt - ar        l   l    x       l foreach println   Result 1 2 3 4 5 6  Prepending  var l   List Int         for x  lt - ar          l  x    l     prepending          l foreach println      Result 6 5 4 1 2 3

User · Answer

This is similar to one of the answers but in different way   scala gt  val x   List 1 2 3  x  List Int    List 1  2  3   scala gt  val y   x     4    Nil y  List Int    List 1  2  3  4

User · Answer

That s because you shouldn t do it  at least with an immutable list   If you really really need to append an element to the end of a data structure and this data structure really really needs to be a list and this list really really has to be immutable then do eiher this    4    List 1 2 3  reverse  reverse   or that   List 1 2 3      List 4

[arrays] Appending an element to the end of a list in Scala

Examples related to arrays

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