R Language Conditional Statements If Else Switch Complete Guide

1. What is the basic syntax of an if statement in R?

Answer: The basic syntax of an if statement in R is as follows:

if (condition) {
  # Code to be executed if the condition is TRUE
}

For example:

x <- 10
if (x > 5) {
  print("x is greater than 5")
}

Here, the message "x is greater than 5" will be printed.

2. How do you use an if-else statement in R?

Answer: The if-else statement allows for conditional execution; if the condition is TRUE, the if block runs, otherwise, the else block executes. The syntax is:

if (condition) {
  # Code to be executed if the condition is TRUE
} else {
  # Code to be executed if the condition is FALSE
}

For example:

x <- 3
if (x > 5) {
  print("x is greater than 5")
} else {
  print("x is not greater than 5")
}

In this case, "x is not greater than 5" is printed since 3 is not greater than 5.

3. Can you explain how to nest if-else statements in R?

Answer: Nesting if-else statements in R allows for multiple condition checks. Nested if-else syntax:

if (condition1) {
  # Code if condition1 is TRUE
} else if (condition2) {
  # Code if condition1 is FALSE and condition2 is TRUE
} else {
  # Code if both conditions are FALSE
}

Example:

x <- 10
if (x > 0) {
  if (x <= 10) {
    print("x is between 1 and 10 inclusive")
  } else {
    print("x is greater than 10")
  }
} else {
  print("x is less than or equal to 0")
}

4. What is the switch statement in R, and how does it work?

Answer: The switch statement in R allows for multi-way branching based on the value of an expression, typically used as an alternative to multiple if-else statements for readability. The syntax:

switch(expression, 
       case1 = val1,
       case2 = val2,
       ...,
       caseN = valN,
       default = default_val)

For example:

action <- "start"
result <- switch(action,
                 start = "Process initiating",
                 stop = "Process terminating",
                 pause = "Process paused",
                 default = "Unknown action")
print(result) # Output: Process initiating

5. Can you provide an example of using switch in place of if-else for categorical data handling?

Answer: Certainly. Here’s an example where switch is used to handle categorical data instead of multiple if-else conditions:

day_of_week <- "Wednesday"
activity <- switch(day_of_week,
                  Monday = "Gym",
                  Tuesday = "Meeting",
                  Wednesday = "Lunch with friends",
                  Thursday = "Conference",
                  Friday = "Weekend prep",
                  "Relax at home")
print(activity) # Output: Lunch with friends

6. What happens if the condition in an if statement is not a logical value?

Answer: If the condition provided to an if statement is not a logical value (TRUE or FALSE), R will issue a warning and typically return FALSE. It's best practice to ensure the condition evaluates to a logical value to avoid unexpected behavior. For example:

x <- 5
if (x = 10) {  # Should use '==' for comparison, not '='
  print("x equals 10")
}

Here, using = instead of == will assign 10 to x and treat the statement as if (10), which is equivalent to if (TRUE).

7. How can you handle multiple conditions in a single if statement?

Answer: You can handle multiple conditions using logical operators like & (and), | (or), && (and for vectors), and || (or for vectors). Here’s how:

• Using & and | for element-wise logical operations:

x <- 10
y <- 20
if (x > 5 & y < 25) {
  print("Both conditions are true")
}

• Using && and || for short-circuit logical operations (evaluate until result is determined):

x <- 10
y <- 20
if (x > 5 && y > 25) {
  print("Both conditions are true")
}

8. How do you use the switch statement with numeric values or other data types besides strings?

Answer: The switch statement in R works not only with strings but also with numerical values and other data types. Here’s how you can use it with numeric values:

score <- 3
grade <- switch(score,
                1 = "Fail",
                2 = "Poor",
                3 = "Average",
                4 = "Good",
                5 = "Excellent",
                "Unknown")
print(grade) # Output: Average

And with factor data type:

status <- factor("Approved")
message <- switch(status,
                  Approved = "Request approved",
                  Denied = "Request denied",
                  Pending = "Request pending",
                  "Unknown status")
print(message) # Output: Request approved

9. Can you provide an example of using nested if and switch in a single function?

Answer: Here’s an example combining both if and switch statements in a single function that categorizes a given number as "Small", "Medium", "Large", and also provides a message if the number is negative:

categorize_number <- function(x) {
  if (x < 0) {
    return("Negative number")
  } else {
    category <- switch(cut(x, breaks = c(-Inf, 10, 50, 100, Inf), labels = c("Small", "Medium", "Large", "Very Large")),
                       Small = "Small number",
                       Medium = "Medium number",
                       Large = "Large number",
                       "Very large number")
    return(category)
  }
}
print(categorize_number(5))     # Output: Small number
print(categorize_number(25))    # Output: Medium number
print(categorize_number(150))   # Output: Very large number
print(categorize_number(-10))   # Output: Negative number

10. What are some common pitfalls or mistakes when using if, else, and switch statements in R?

Answer: Common mistakes when using if, else, and switch statements in R include:

• Using = instead of == for testing equality.
• Forgetting to include else for all cases where an alternative execution is expected.
• Improper handling of multiple conditions with logical operators, which can lead to incorrect results.
• Using switch without a default case, leading to unexpected results when no match is found.
• Misunderstanding the difference between &, &&, |, and || and their implications for performance and evaluation. Example of common mistakes: