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Arrays

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Arrays are a fundamental data structure in Ruby that allow you to store and manipulate collections of data. In this section, we will cover the basics of arrays, including how to create them, access their elements, and perform common operations.

What is an Array?

An array is an ordered collection of elements, which can be of any type (e.g., integers, strings, objects). Arrays are indexed, meaning each element in the array has a specific position, starting from 0.

Creating Arrays

You can create arrays in Ruby using square brackets [] or the Array class.

# Using square brackets
numbers = [1, 2, 3, 4, 5]

# Using the Array class
words = Array.new
words = ["hello", "world"]

Accessing Elements

You can access elements in an array using their index. Remember, array indices start at 0.

numbers = [1, 2, 3, 4, 5]

# Accessing the first element
first_number = numbers[0]  # => 1

# Accessing the last element
last_number = numbers[-1]  # => 5

Modifying Arrays

You can modify elements in an array by assigning new values to specific indices.

numbers = [1, 2, 3, 4, 5]

# Changing the second element
numbers[1] = 10  # numbers is now [1, 10, 3, 4, 5]

Common Array Methods

Ruby provides a variety of methods to manipulate arrays. Here are some of the most commonly used ones:

Method Description Example
push Adds an element to the end of the array numbers.push(6)
pop Removes the last element from the array numbers.pop
shift Removes the first element from the array numbers.shift
unshift Adds an element to the beginning of the array numbers.unshift(0)
length Returns the number of elements in the array numbers.length
include? Checks if an element is present in the array numbers.include?(3)
sort Returns a new array with the elements sorted numbers.sort
reverse Returns a new array with the elements reversed numbers.reverse
each Iterates over each element in the array `numbers.each {

Practical Examples

Example 1: Adding Elements

fruits = ["apple", "banana", "cherry"]

# Adding an element to the end
fruits.push("date")  # => ["apple", "banana", "cherry", "date"]

# Adding an element to the beginning
fruits.unshift("elderberry")  # => ["elderberry", "apple", "banana", "cherry", "date"]

Example 2: Removing Elements

fruits = ["apple", "banana", "cherry", "date"]

# Removing the last element
fruits.pop  # => "date", fruits is now ["apple", "banana", "cherry"]

# Removing the first element
fruits.shift  # => "apple", fruits is now ["banana", "cherry"]

Example 3: Iterating Over an Array

numbers = [1, 2, 3, 4, 5]

# Using each to iterate over the array
numbers.each do |number|
  puts number * 2
end

# Output:
# 2
# 4
# 6
# 8
# 10

Exercises

Exercise 1: Basic Array Operations

  1. Create an array called colors with the elements "red", "green", and "blue".
  2. Add "yellow" to the end of the array.
  3. Remove the first element from the array.
  4. Check if the array includes "green".
  5. Print the length of the array.

Solution:

# Step 1
colors = ["red", "green", "blue"]

# Step 2
colors.push("yellow")

# Step 3
colors.shift

# Step 4
includes_green = colors.include?("green")

# Step 5
length_of_colors = colors.length

# Output the results
puts "Colors: #{colors}"
puts "Includes 'green': #{includes_green}"
puts "Length of colors array: #{length_of_colors}"

Exercise 2: Iterating and Modifying Arrays

  1. Create an array called numbers with the elements 1, 2, 3, 4, and 5.
  2. Use the each method to iterate over the array and print each element multiplied by 3.
  3. Use the map method to create a new array with each element squared.

Solution:

# Step 1
numbers = [1, 2, 3, 4, 5]

# Step 2
numbers.each do |number|
  puts number * 3
end

# Step 3
squared_numbers = numbers.map { |number| number ** 2 }

# Output the results
puts "Squared numbers: #{squared_numbers}"

Common Mistakes and Tips

  • Index Out of Bounds: Trying to access an index that doesn't exist in the array will return nil. Always ensure the index is within the array's range.
  • Mutating Methods: Some methods modify the array in place (e.g., push, pop), while others return a new array (e.g., sort, reverse). Be mindful of which type you are using.
  • Iterating with each: The each method is commonly used for iteration, but remember it does not modify the original array. Use map if you need to transform the array.

Conclusion

Arrays are a versatile and essential part of Ruby programming. Understanding how to create, access, and manipulate arrays will greatly enhance your ability to work with collections of data. In the next section, we will explore another important data structure in Ruby: Hashes.

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