Return Values
Concept
In R, return values are crucial as they determine what a function outputs after execution. You can specify what a function should return using the return() function, or, if omitted, R returns the last evaluated expression by default.
Syntax
function_name <- function(arguments) {
# Function body
return(value) # Specifies what to return
}
Basic Example
# Define the function
add_numbers <- function(a, b) {
sum <- a + b
return(sum)
}
# Function call
result <- add_numbers(5, 3) # 8
print(result)
Explanation:
- The add_numbers function calculates the sum of a and b and returns it using return(sum).
- The function call add_numbers(5, 3) returns 8.
Default Return Value
If return() is not used, R returns the last value evaluated in the function.
# Define the function without return()
subtract_numbers <- function(a, b) {
difference <- a - b
difference # The last evaluated value is returned
}
# Function call
result <- subtract_numbers(10, 4) # 6
print(result)
Explanation:
- Here, subtract_numbers returns the value of difference even though return() is not explicitly used.
Multiple Return Values
R functions can return multiple values by encapsulating them in a list.
# Define the function
statistics <- function(x) {
mean_val <- mean(x)
sd_val <- sd(x)
return(list(mean = mean_val, sd = sd_val))
}
# Function call
result <- statistics(c(1, 2, 3, 4, 5))
print(result)
Explanation:
- The statistics function returns a list containing the mean and standard deviation of the input values.
- list(mean = mean_val, sd = sd_val) creates a list with two named elements: mean and sd.
Return Value with Conditions
You can use conditional statements to determine what the function returns.
# Define the function
categorize_number <- function(x) {
if (x > 0) {
return("Positive")
} else if (x < 0) {
return("Negative")
} else {
return("Zero")
}
}
# Function calls
print(categorize_number(10)) # "Positive"
print(categorize_number(-5)) # "Negative"
print(categorize_number(0)) # "Zero"
Explanation:
- The categorize_number function returns a different string based on whether x is positive, negative, or zero.
Implicit Return Value
If no explicit return() is used, the last evaluated expression is returned. This can simplify functions.
# Define the function
multiply_numbers <- function(a, b) {
a * b # The last evaluated expression is returned
}
# Function call
result <- multiply_numbers(4, 5) # 20
print(result)
Explanation:
- Here, a * b is the last expression evaluated, so it is automatically returned.
Best Practices
- Clarity: Use return() to make it clear what your function returns, especially if multiple values are computed.
- Consistency: Be consistent in whether you use return(). Choose to use or omit it based on code readability and clarity.