lapply Function in R: How to Use The lapply Function

In this tutorial, you will understand the lapply function and how to apply it to a list or vector in R. By following along, you will become proficient in using this critical function in the R programming language.

What is the lapply Function in R?

The lapply() is a function in the base package of R that applies a function to each element of a list or vector that returns a list with the same length as the input, but with the elements being the results of applying the function to the corresponding element of the input.

You can see the syntax of this function below.

lapply Function in R: The Syntax

lapply(DATA, FUN, ...)

Parameters:

• DATA: is a list or vector, data frame, …
• FUN: is the function to be applied to each element of DATA

How to use the lapply function in R?

lapply function with a vector

To use the lapply function, first, we need to create a vector and a function. You can create a fake vector and function as follows:

# Create a vector
x <- c(5, 9, 6)

# Create a function: square function
func <- function(x){
    x^2
}

We will apply the ‘func’ function to each element of the vector x and return a new vector with the square of each element:

# Create a vector
x <- c(5, 9, 6)

# Create a function: square function
func <- function(x) {
    x^2
}

# Calculate the square of each element
lapply(x, func)

Output

[[1]]
[1] 25

[[2]]
[1] 81

[[3]]
[1] 36

lapply function with a list

Here, we will create a list for this example.

# Create a list
x <- c(8, 5, 6, 2)

# View a list
x

Now, we will use the lapply function with this list, and log function in R. Check out the code example below

# Create a list
x <- c(8, 5, 6, 2)

# Calculate the square of each element
lapply(x,log)

Output

[[1]]
[1] 2.079442

[[2]]
[1] 1.609438

[[3]]
[1] 1.791759

[[4]]
[1] 0.6931472

lapply function with a data frame

In this example, we have a data frame below

# Create a data frame
df <- data.frame(
    Name = c("Linda R. Mancuso", "Mark C. Arnold", "Janice E. Clark"),
    ID = c(1, 2, 3),
    Math = c(8, 7, 9),
    English = c(7, 8, 9)
)

# View a data frame
df

We will use the lapply function in R to calculate the mean of the Math and English columns of the data frame above. See the example below.

# Create a data frame
df <- data.frame(
    Name = c("Linda R. Mancuso", "Mark C. Arnold", "Janice E. Clark"),
    ID = c(1, 2, 3),
    Math = c(8, 7, 9),
    English = c(7, 8, 9)
)

# Create a function to use the quick lapply function
lapp <- function(x) {
    return(lapply(x, mean))
}

# Calculate the mean
cat("The mean of the Math columns is:\n")
lapply(df$Math, mean)

cat("The mean of the English columns is:\n")
lapply(df$Math, mean)

Output

The mean of the Math columns is:
[[1]]
[1] 8

[[2]]
[1] 7

[[3]]
[1] 9
The mean of the English columns is:
[[1]]
[1] 8

[[2]]
[1] 7

[[3]]
[1] 9

Summary

In this article, we learned how to utilize the lapply function in R to apply a specific function to every element within a list or vector. If you have any questions or need further clarification, please leave a comment below. 

We hope you have a great day!

Scott Miller

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