# How to Use the lapply() Function in R

The lapply() function in R is “used to apply a function to a list, data frame or a vector, returning a list of the same length“.

### Syntax

``lapply(X, FUN)``

### Parameters

1. X: A vector or an object.
2. FUN: Function applied to each element of X.

## Example 1: Iterate over a vector using the lapply() function

``````movies <- c("Titanic", "BATMAN", "Venom", "Conjuring")
movies_lower <- lapply(movies, tolower)

print(str(movies_lower)) ``````

Output

``````List of 4
\$ : chr "titanic"
\$ : chr "batman"
\$ : chr "venom"
\$ : chr "conjuring"
NULL``````

First, we defined a vector and used the lapply() function to convert all the elements to the small case.

## Example 2: Iterate over a list using the lapply() function

``````list_new <- list(
A = c(11, 19, 21, 46),
B = data.frame(x = 1:5, y = c(1, 2, 3, 7, 8))
)

lapply(list_new, sum)
``````

Output

``````\$A
 97

\$B
 36``````

## Example 3: Use lapply() function with multiple arguments

``````list_new <- list(
A = c(11, 19, 21, 46),
B = c(1, 2, 3, 4)
)

lapply(list_new,
quantile,
probs = c(0.25, 0.50)
)``````

Output

``````\$A
25% 50%
17 20

\$B
25% 50%
1.75 2.50``````

## Example 4: Use lapply() with a custom function

You can also apply a custom function with the “lapply()” function.

``````vec <- 1:3

# Function to calculate the third power
fun <- function(x) {
x ^ 3
}

# Applying our own function
lapply(vec, fun)
``````

Output

``````[]
 1

[]
 8

[]
 27
``````