Scala Scala Collections

Question 1

What is the difference between a Scala `List` and `Vector`?

Accepted Answer

List has O(1) prepend; Vector has O(log n) random access and is better for large collections

Answer

Scala's immutable `List` provides O(1) prepend but O(n) random access, while `Vector` provides effectively O(1) random access for large collections.

Question 2

How do you add an element to the front of a Scala immutable List?

Accepted Answer

elem :: list

Answer

The `::` cons operator prepends an element to a Scala List, returning a new List with the element at the front.

Question 3

What does `groupBy` do on a Scala collection?

Accepted Answer

Groups elements into a Map by the result of a key function

Answer

`groupBy` applies a function to each element and returns a `Map` from keys to collections of elements sharing that key.

Question 4

Which Scala collection type guarantees uniqueness of elements?

Accepted Answer

Set

Answer

Scala's `Set` enforces element uniqueness, ignoring duplicate insertions based on the `equals` and `hashCode` of elements.

Question 5

What is the purpose of `foldLeft` in Scala?

Accepted Answer

Accumulates a result from left to right using a binary function and an initial value

Answer

`foldLeft(init)(f)` starts with an initial value and applies a binary function from left to right across the collection.

Scala Practice Test