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Introduction to Collections

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In this section, we will explore the fundamental concepts of collections in Scala. Collections are essential for handling groups of data efficiently and are a cornerstone of both functional and object-oriented programming in Scala. We will cover the following topics:

  1. Overview of Collections
  2. Immutable vs. Mutable Collections
  3. Common Collection Types
  4. Basic Operations on Collections

  1. Overview of Collections

Scala collections provide a rich set of data structures to store and manipulate data. They are divided into three main categories:

  • Sequences: Ordered collections of elements.
  • Sets: Unordered collections of unique elements.
  • Maps: Collections of key-value pairs.

  1. Immutable vs. Mutable Collections

Scala collections can be either immutable or mutable. Understanding the difference is crucial for writing efficient and safe code.

Immutable Collections

Immutable collections cannot be modified after they are created. Any operation that modifies an immutable collection returns a new collection with the changes applied.

Advantages:

  • Thread-safe: No need for synchronization.
  • Easier to reason about: No side effects.

Examples:

  • List
  • Vector
  • Set
  • Map

Mutable Collections

Mutable collections can be modified in place. They are useful when performance is critical, and you need to update the collection frequently.

Advantages:

  • Performance: In-place updates can be faster.

Examples:

  • ArrayBuffer
  • ListBuffer
  • HashSet
  • HashMap

  1. Common Collection Types

Sequences

Sequences are ordered collections of elements. The most common sequence types are:

  • List: An immutable linked list.
  • Array: A mutable, fixed-size array.
  • Vector: An immutable, indexed sequence.

Sets

Sets are collections of unique elements. The most common set types are:

  • Set: An immutable set.
  • HashSet: A mutable set.

Maps

Maps are collections of key-value pairs. The most common map types are:

  • Map: An immutable map.
  • HashMap: A mutable map.

  1. Basic Operations on Collections

Let's look at some basic operations you can perform on collections.

Creating Collections

// Immutable List
val fruits = List("Apple", "Banana", "Cherry")

// Mutable ArrayBuffer
import scala.collection.mutable.ArrayBuffer
val numbers = ArrayBuffer(1, 2, 3, 4, 5)

Accessing Elements

// Accessing elements in a List
val firstFruit = fruits(0) // "Apple"

// Accessing elements in an ArrayBuffer
val firstNumber = numbers(0) // 1

Adding Elements

// Adding elements to an immutable List (returns a new List)
val moreFruits = fruits :+ "Date"

// Adding elements to a mutable ArrayBuffer (modifies in place)
numbers += 6

Removing Elements

// Removing elements from an immutable List (returns a new List)
val lessFruits = fruits.filterNot(_ == "Banana")

// Removing elements from a mutable ArrayBuffer (modifies in place)
numbers -= 1

Iterating Over Collections

// Iterating over a List
for (fruit <- fruits) {
  println(fruit)
}

// Iterating over an ArrayBuffer
numbers.foreach(println)

Practical Exercise

Exercise 1: Working with Lists

  1. Create an immutable list of integers from 1 to 10.
  2. Add the number 11 to the list.
  3. Remove the number 5 from the list.
  4. Print each element of the final list.

Solution

// Step 1: Create an immutable list of integers from 1 to 10
val numbers = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

// Step 2: Add the number 11 to the list
val updatedNumbers = numbers :+ 11

// Step 3: Remove the number 5 from the list
val finalNumbers = updatedNumbers.filterNot(_ == 5)

// Step 4: Print each element of the final list
finalNumbers.foreach(println)

Exercise 2: Working with Mutable Collections

  1. Create a mutable ArrayBuffer of strings with the names of three fruits.
  2. Add two more fruit names to the ArrayBuffer.
  3. Remove one fruit name from the ArrayBuffer.
  4. Print each element of the final ArrayBuffer.

Solution

import scala.collection.mutable.ArrayBuffer

// Step 1: Create a mutable ArrayBuffer of strings with the names of three fruits
val fruits = ArrayBuffer("Apple", "Banana", "Cherry")

// Step 2: Add two more fruit names to the ArrayBuffer
fruits += "Date"
fruits += "Elderberry"

// Step 3: Remove one fruit name from the ArrayBuffer
fruits -= "Banana"

// Step 4: Print each element of the final ArrayBuffer
fruits.foreach(println)

Conclusion

In this section, we introduced the concept of collections in Scala, differentiating between immutable and mutable collections. We explored common collection types such as sequences, sets, and maps, and demonstrated basic operations on these collections. Understanding these fundamentals will prepare you for more advanced topics in Scala collections and data structures. In the next section, we will dive deeper into specific collection types like Lists and Arrays.

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