How to Use lapply() Function with Multiple Arguments in R

The lapply() function in R is one of the quintessential tools for data manipulation and transformation. It is a member of the family of apply functions (apply, lapply, sapply, etc.) that aim to avoid explicit loops and make code more efficient and readable. While its basic usage is relatively straightforward, applying lapply() with multiple arguments can sometimes be challenging for those who are new to R or data manipulation. This article aims to provide a comprehensive guide on using lapply() in complex scenarios, specifically when you need to pass multiple arguments to the function that lapply() is applying.

Table of Contents

1. Introduction to lapply()
2. Basic Usage
3. Using lapply() with a Single Argument Function
4. Using lapply() with Multiple Argument Functions
   • Positional Arguments
   • Named Arguments
   • Ellipsis (...)
5. Common Pitfalls
6. Advanced Scenarios
   • Using Anonymous Functions
   • Using do.call()
   • Environment and Scope
7. Conclusion

1. Introduction to lapply( )

The lapply() function stands for List Apply. It applies a function to each element of a list (or a vector or a data frame) and returns a list of the same length as the input. Its basic syntax is:

lapply(X, FUN, ...)

• X: A list or a vector to iterate over.
• FUN: The function to apply.
• ...: Additional arguments to FUN.

2. Basic Usage

Let’s start by looking at a simple example:

numbers <- 1:5
result <- lapply(numbers, function(x) x * 2)

Here, lapply() takes a numeric vector from 1 to 5 and a function that multiplies its input by 2. The result is a list where each element is twice the corresponding element in the input vector.

3. Using lapply( ) with a Single Argument Function

When you’re dealing with a function that takes a single argument, using lapply() is straightforward:

# Function definition
square <- function(x) {
  return(x * x)
}

# Using lapply
result <- lapply(1:5, square)

4. Using lapply( ) with Multiple Argument Functions

4.1 Positional Arguments

If the function you want to apply takes multiple arguments, you can pass the additional arguments after specifying the function name:

# Function definition
power <- function(x, exponent) {
  return(x^exponent)
}

# Using lapply
result <- lapply(1:5, power, exponent = 2)

4.2 Named Arguments

In some cases, using named arguments can make the code more readable:

result <- lapply(1:5, power, exponent = 3)

4.3 Ellipsis (. . . )

You can also use the ellipsis (...) to pass multiple arguments:

# Function definition with ellipsis
multiply_add <- function(x, multiplier, adder) {
  return((x * multiplier) + adder)
}

# Using lapply with multiple additional arguments
result <- lapply(1:5, multiply_add, multiplier = 2, adder = 3)

5. Common Pitfalls

Watch out for:

• Using functions with side effects
• Misaligned argument lengths
• Wrong argument types

6. Advanced Scenarios

6.1 Using Anonymous Functions

You can use an anonymous function to wrap the main function, providing a convenient way to pass multiple arguments:

result <- lapply(1:5, function(x) power(x, 2))

6.2 Using do.call( )

do.call() can be used within lapply() to call a function with arguments supplied as a list:

result <- lapply(1:5, function(x) do.call(power, list(x, 2)))

6.3 Environment and Scope

Be mindful of the function environment when using lapply(). Variables defined outside the function may not behave as you expect.

7. Conclusion

Using lapply() with multiple arguments can be done in several ways, from using positional arguments to employing anonymous functions or do.call() for more advanced scenarios.