How can I print the first element in list using Scala?
For example in Python I can just write:
>>>l = [1,2,3,4]
>>>one = l[0]
>>>print one
How can I do that on Scala
Thanks.
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4 Answers
The element can be retrieved using index-based access like this:
object ListDemo extends App {
val lst = List(1, 2, 3)
println(lst(0)) // Prints specific value. In this case 1.
// Number at 0 position.
println(lst(1)) // Prints 2.
println(lst(2)) // Prints 3.
}
Comments
Basically, your python code is equivalent of:
scala> val l = 1 :: 2 :: 3 :: 4 :: Nil
l: List[Int] = List(1, 2, 3, 4)
scala> val one = l.head
one: Int = 1
scala> println(one)
1
(Run in the scala interpreter.)
Here is the documentation about Scala's List.
It was asked as a subsidiary question «how do I display each element?».
Here is a recursive implementation using pattern matching:
scala> def recPrint(xs: List[Int]) {
| xs match {
| case Nil => // nothing else to do
| case head :: tail =>
| println(head)
| recPrint(tail)
| }}
recPrint: (xs: List[Int])Unit
scala> recPrint(l)
1
2
3
4
As David Weber pointed out in the comments, if you cannot use a recursive algorithm to visit your list's elements then you should consider using another container, because accessing the i-th element of a List takes O(N).
4 Comments
Michael
yeah but how can i print second or third element in list?
Hiura
Well, that was another question ;-) You can either use the
apply method (like in Brano88's answer), or recurse on the tail of the list.
David Weber
If you can traverse the list from head to tail, then recurse away. If not, you are using the wrong data structure as apply is O(N) for lists. Use Vector or Array instead.
Hiura
@DavidWeber that's a very good point. I've included it in my answer. ;-)
Answer can easily be found in scaladoc for list
def head: A
Selects the first element of this list.
Comments
Here we have created an object (Object name: TestList) which containing variable myList.
scala> object TestList{
| def main(args: (Array[String])){
| var myList = List(1,2,3,4,5)
| println("Complete List is : "+myList)
| println("Reverse List : "+myList.reverse)
| println("Print Send Element from list : " + myList(1))
| println("Print First three element : "+ myList.take(3))
| println("Remove First two element : "+myList.drop(2))
| }
| }
defined object TestList
Calling object with main Method
scala> TestList.main(Array(""))
OUTPUT:
Complete List is : List(1, 2, 3, 4, 5)
Reverse List : List(5, 4, 3, 2, 1)
Print Send Element from list : 2
Print First three element : List(1, 2, 3)
Remove First two element : List(3, 4, 5)
1 Comment
sɐunıɔןɐqɐp
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