length() function gets or sets the length of a vector (list) or other objects.

Get vector length:

> x <- c(1,2,5,4,6,1,22,1)
> length(x)

[1] 8

Set vector length:

> length(x) <- 4
> x

[1] 1 2 5 4

nchar() function can be used to get the length of a string:

> str <- "this is a string"
> length(str)
[1] 1
> nchar(str)
[1] 16

length is the intrinsic attribute of all R objects. To get the length of a list:

> y <- list(batch=3,label="Lung Cancer Patients", subtype=c("A","B","C"))
> y

$batch
[1] 3
$label
[1] "Lung Cancer Patients"
$subtype
[1] "A" "B" "C"

> is.list(y)

[1] TURE

> length(y)

[1] 3

If the parameter is a matrix or dataframe, it returns the number of variables:

> length(BOD)

[1] 2

> BOD

Time demand
1 1 8.3
2 2 10.3
3 3 19.0
4 4 16.0
5 5 15.6
6 7 19.8

When resets a list or matrix, if the list is shortened, extra values will be discarded, if the list is lengthened, NAs (or nul) is added to the list.

> length(BOD) <- 1
> BOD

$Time
[1] 1 2 3 4 5 7

> length(BOD) <- 3
> BOD

$Time
[1] 1 2 3 4 5 7
$demand
[1] 8.3 10.3 19.0 16.0 15.6 19.8
[[3]]
NULL

length() function can be used for all R objects. For an environment it returns the object number in it. NULL returns 0. Most other objects return length 1.