length()

length(x)

Returns: integer · Updated March 13, 2026 · Base Functions

base vector length

The length() function returns the number of elements in a vector, the number of components in a list, or the length of a string. It is one of the most frequently used functions in R for determining the size of objects. You can also use length<- to assign a new length to an object, which is useful for truncating or extending vectors.

Syntax

length(x)
length(x) <- value

Parameters

Parameter	Type	Default	Description
`x`	any R object	N/A	A vector, list, matrix, data frame, or other R object
`value`	non-negative integer	N/A	New length to assign (only when using `length<-`)

Examples

Basic usage with vectors

# Numeric vector
x <- c(1, 2, 3, 4, 5)
length(x)
# [1] 5

# Character vector
words <- c("apple", "banana", "cherry")
length(words)
# [1] 3

# Empty vector
empty <- character(0)
length(empty)
# [1] 0

Working with lists

my_list <- list(a = 1, b = 2, c = 3)
length(my_list)
# [1] 3

# Nested list
nested <- list(list(1, 2), list(3, 4, 5))
length(nested)
# [1] 2

Setting length

x <- 1:10
length(x)
# [1] 10

# Truncate to 5 elements
length(x) <- 5
x
# [1] 1 2 3 4 5

# Extend to 10 elements (fills with NA)
length(x) <- 10
x
# [1]  1  2  3  4  5 NA NA NA NA NA

Common Patterns

Looping over elements:

for (i in 1:length(x)) {
  print(x[i])
}

Checking if a vector is empty:

if (length(x) == 0) {
  message("Vector is empty")
}

Dynamic vector growth (inefficient - pre-allocate instead):

result <- numeric(0)
for (i in 1:100) {
  length(result) <- i
  result[i] <- i^2
}