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Scala Array, Lists and Tuples

Array

  • We know that we can parameterize a class instantiation. Suppose that instantiation takes a type. What is the syntax for this?

    • We use square brackets
    • Example: var arr = new Array[Int](5)
    • Here we have 2 parameters
      • Type of Int
      • Size of 5
    • Size is parameterized the normal way using parenthesis

  • What is the type of this variable var x = new Array[Int](420)

    • Array[Int]

  • Do the size of an array contribute to its type?

    • No
    • Suppose we have a typeof function in scala
    • Then typeof(new Array[String](10)) == typeof(new Array[String](25))

  • How to use the to method?

    • for(i <- 1 to 10)

  • Explain how to is actually a method?

    • for(i <- 1 to 10) is expanded to for (i <- (1).to(10))

  • Why is operator overloading not supported in scala?

    • Scala doesn’t have any operators
    • Operators are actually functions
    • 3 + 2 is actually (3).+(2)
    • Here (3) is an object literal of the class Int
    • + is a method
    • 2 is passed as an argument

  • Under the hood how are array accesses done?

    • Arrays are a class just like every other thing in scala
    • arr(5) is actually arr.apply(5)
val arr = new Array[Int](5)
arr(0) = 69
  • Consider the above code snippet.Will this produce an error? Explain how the second line is interpreted under the hood
    • No
    • Even though arr is declared as a val when we are assigning arr(0) to 69 we are not actually reassigning arr
    • arr = new Array[Int](69) will cause an error as we are reassigning arr
    • arr(0) = 69 is actually arr.update(0, 69). So we are just calling a method.
  • Initialize an array using factory methods
    • var x = Array("Hello", "to", "you")

List

  • How to create a new list
    • var x = List(1, 2, 3)
  • How to concatenate two lists?
    • Using the ::: method
  • How to insert an element in the front of a list
    • ::. Cons operator
  • Empty list is represented as ?
    • Nil
  • Suppose I have a list list and I want to count the number of element that pass a certain predicate p. How do I do this?
    • list.count(p)
  • How to get the last n elements of a list?
    • list.drop(n)
  • How to get the first n elements of a list?
    • list.dropRight(n)
  • How to search a list for an element?
    • list.exists(s => s == "s")
  • Get the elements that pass a certain predicate?
    • list.filter(even)
  • Get all the elements except the last
    • list.init
  • Convert a list to string
    • list.mkString(sep)
  • How will you sort a list in alphabetical order based on the first letter
    • list.sort((s, t) => s.charAt(0).toLower < t.charAt(0).toLower)
  • Create a list of 10 9s
    • List.fill(10)(2)
  • Compute the sum of a list using foreach
    • var sum = 0
    • list.foreach(sum += _)
  • In the context of a Char, is toLower a property or a method
    • Property
  • Are lists mutable?
    • No
  • How to get a mutated version of a list?
    • Using the updated() method

Tuple

  • What is the principal difference between lists and tuples?
    • Tuples can contain multiple types
  • How to create a new tuple?
    • (1, 2, "Hello")
  • Access the $n^{th}$ member of a tuple
    • tuple._n
  • What sort of indexing do tuples follow?
    • one-based index
  • Imagine there is a function typeof. typeof((1, 2)) == typeof((1, 2, 3))
    • No
    • In tuples the number of elements is also included in the type
  • Why can’t we use the apply method used to access elements in a list/array for a tuple?
    • apply methods always returns a value of the same type
    • That is not the case with tuples. So we need a new method
  • How do you iterate a tuple
    • tuple.productIterator.foreach(f)