| length {base} | R Documentation |
Length of an Object
Description
Get or set the length of vectors (including lists) and factors, and of any other R object for which a method has been defined.
Usage
length(x)
length(x) <- value
Arguments
x |
an R object. For replacement, a vector or factor. |
value |
a non-negative integer or double (which will be rounded down). |
Details
Both functions are generic: you can write methods to handle specific
classes of objects, see InternalMethods. length<- has a
"factor" method.
The replacement form can be used to reset the length of a vector. If
a vector is shortened, extra values are discarded and when a vector is
lengthened, it is padded out to its new length with NAs
(nul for raw vectors).
Both are primitive functions.
Value
The default method for length currently returns a non-negative
integer of length 1, except for vectors of more than
2^{31}-1 elements, when it returns a double.
For vectors (including lists) and factors the length is the number of
elements. For an environment it is the number of objects in the
environment, and NULL has length 0. For expressions and
pairlists (including language objects and dot-dot-dot lists) it is the
length of the pairlist chain. All other objects (including functions)
have length one: note that for functions this differs from S.
The replacement form removes all the attributes of x except its
names, which are adjusted (and if necessary extended by "").
Warning
Package authors have written methods that return a result of length
other than one (Formula) and that return a vector of type
double (Matrix), even with non-integer values
(earlier versions of sets). Where a single double value is
returned that can be represented as an integer it is returned as a
length-one integer vector.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
nchar for counting the number of characters in character
vectors, lengths for getting the length of every element
in a list.
Examples
length(diag(4)) # = 16 (4 x 4)
length(options()) # 12 or more
length(y ~ x1 + x2 + x3) # 3
length(expression(x, {y <- x^2; y+2}, x^y)) # 3
## from example(warpbreaks)
require(stats)
fm1 <- lm(breaks ~ wool * tension, data = warpbreaks)
length(fm1$call) # 3, lm() and two arguments.
length(formula(fm1)) # 3, ~ lhs rhs