Part I: Functions and Control Structures

Writing and using functions

Example: A simple function to calculate the square of a number

\[ f(x) = x^2 \]

square_function <- function(x) {
  return(x^2)
}

# Using the function
result <- square_function(4)
print(result)
#> [1] 16

Exercise 1

Task: Write and Use a Function Objective: Create a function that calculates the cube of a number and use this function to calculate the cube of 3.

Hint: Use the structure of the square_function as a template.

The reason why this is useful, is because functions are used for anything we want, R functions are just similar to the one we have just created, optimized for the specific tasks they were designed for .

We now create a more complex function , one that takes a vector , finds the mean , standard deviation and the histogram

analyze_vector <- function(x, plot_title = "Histogram") {
  # Check if the input is numeric
  if (!is.numeric(x)) {
    stop("Input must be a numeric vector")
  }
  
  # Calculate mean and standard deviation
  mean_value <- mean(x)
  std_value <- sd(x)
  
  # Output the mean and std
  cat("Mean:", mean_value, "\n")
  cat("Standard Deviation:", std_value, "\n")
  
  # Create a histogram
  hist(x, main = plot_title, xlab = "Values", col = "lightblue", border = "black")
  
  # Return a list containing the mean and std
  return(list(mean = mean_value, std = std_value))
}

# Example usage with the mtcars$mpg vector
result <- analyze_vector(mtcars$mpg, "MPG Histogram")
#> Mean: 20.09062 
#> Standard Deviation: 6.026948

Exercise 2

Task: Analyze a Numeric Vector Objective: Write a function named summarize_vector that takes a numeric vector as input and calculates the median, variance, and creates a boxplot. The function should print the median and variance, and return them as a list. Use the airquality$Ozone data for analysis.

Hint: Similar to analyze_vector, check if the input is numeric and use median, var, and boxplot functions.

If statements and loops (for and while)

# Example: Using if statement
number <- 5
if (number > 0) {
  print("Positive number")
} else {
  print("Non-positive number")
}
#> [1] "Positive number"

Exercise 3

Task: Using if Statements Objective: Create an R script that checks if a number is negative, zero, or positive and prints an appropriate message. Test your script with the number -4.

Hint: Use an if statement followed by else if and else.

Example:

For loop to calculate the factorial of a number

factorial_function <- function(n) {
  result <- 1
  for (i in 1:n) {
    result <- result * i
  }
  return(result)
}

factorial_of_5 <- factorial_function(5)
print(factorial_of_5)
#> [1] 120

Exercise 4

Task: For Loop Objective: Write a function using a for loop that calculates the sum of squares of numbers from 1 to n. Use this function to calculate the sum of squares for n=10.

Hint: Iterate from 1 to n, and keep adding the square of each number to a result variable.

Example:

While loop to find the first square number greater than 100

number <- 1
while (number^2 <= 100) {
  number <- number + 1
}
print(paste("First square number greater than 100 is:", number^2))
#> [1] "First square number greater than 100 is: 121"

Exercise 5

Task: While Loop Objective: Write a script using a while loop that finds the smallest number whose cube is greater than 100. Print the number and its cube.

Hint: Increment a number starting from 1, and check if its cube is greater than 100 in the while loop condition.