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

List is mutable; Vector is immutable

Answer

Vector only holds Int values

Answer

List supports parallel operations; Vector does not

Question 2

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

Accepted Answer

elem :: list

Answer

list.add(elem)

Answer

list.prepend(elem)

Answer

list + elem

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

Sorts elements

Answer

Removes duplicates

Answer

Partitions into exactly two groups

Question 4

Which Scala collection type guarantees uniqueness of elements?

Accepted Answer

Set

Answer

Seq

Answer

List

Answer

Queue

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

Folds a list in half

Answer

Flattens a nested list

Answer

Folds the type hierarchy

Question 6

What does `partition` return on a Scala collection?

Accepted Answer

A tuple of two collections: elements satisfying a predicate and those that don't

Answer

A single filtered collection

Answer

A Map from Boolean to collections

Answer

The first element matching a predicate