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関数の書き込み
In R, functions are first-class citizens (objects in their own right) and allow you to structure your code into modular, reusable, and well-organized blocks.
Defining a Function
To define a function, use the function keyword and assign the created object to a variable (the function name) using the assignment operator <-:
# Simple function definition
greet_user <- function() {
print("Hello, User!")
}
# Invoking the function
greet_user()
Parameters and Return Values
Functions can accept one or more parameters. To explicitly return a value, use the return() function. If return() is omitted, R will automatically return the value of the last evaluated expression in the function body.
# Function that adds two numbers and returns the result
add_numbers <- function(a, b) {
sum_result <- a + b
return(sum_result)
}
total <- add_numbers(5, 7)
print(total) # Prints 12
Default Arguments
You can specify default values for a function's parameters. If the argument is not provided when the function is invoked, R will use the default value:
# The function uses a default discount rate of 10% (0.10)
apply_discount <- function(price, discount = 0.10) {
discounted_price <- price * (1 - discount)
return(discounted_price)
}
# Uses the default (10%)
print(apply_discount(100)) # Prints 90
# Specifies a custom discount (20%)
print(apply_discount(100, 0.20)) # Prints 80
Returning Multiple Values with Lists
Since a function in R can only return a single object directly via return(), if we need to return multiple values (possibly of different types or lengths), we can bundle them inside a list (list):
get_stats <- function(v) {
stats <- list(
mean_val = mean(v),
max_val = max(v)
)
return(stats)
}
results <- get_stats(c(10, 20, 30))
print(results$mean_val) # Prints 20
Anonymous Functions and sapply
Anonymous functions (functions without a name defined inline) are extremely useful when paired with functions like sapply() to apply quick transformations on elements of a vector or list.
In modern R (from version 4.1.0 onwards), you can define anonymous functions using the shorthand syntax \(x) in addition to the classic function(x):
v <- c(1, 2, 3)
# Using sapply with a classic anonymous function
sapply(v, function(x) x^2) # 1 4 9
# Using sapply with shorthand syntax (R >= 4.1.0)
sapply(v, \(x) x^2) # 1 4 9
Try it yourself
Define a function named double_value that accepts a single argument x and returns its double (x * 2) using return().
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Usa la sintassi: double_value <- function(x) { return(x * 2) }
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Define a function named calculate_area that accepts two arguments: width and height. The function must return their product using return().
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Define the function with parameters width and height, and return width * height.
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Define a function named calculate_tax that accepts a required argument amount and an optional argument rate with a default value of 0.22. Return the product amount * rate.
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Usa: calculate_tax <- function(amount, rate = 0.22) { return(amount * rate) }
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Define a function named analyze_vector that accepts a vector v. The function must return a list containing two elements named sum (the sum of the vector, calculated with sum(v)) and len (the length of the vector, calculated with length(v)).
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Use the syntax: analyze_vector <- function(v) { return(list(sum = sum(v), len = length(v))) }
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Given the vector v, use the sapply() function with an anonymous function to triple the value of each element (multiplying it by 3). Save the result in the variable tripled.
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Use: tripled <- sapply(v, function(x) x * 3)
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