length {base} | R Documentation |
Get or set the length of vectors (including lists) and factors, and of any other R object for which a method has been defined.
length(x)
length(x) <- value
x |
an R object. For replacement, a vector or factor. |
value |
a non-negative integer or double (which will be rounded down). |
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 NA
s
(nul
for raw vectors).
Both are primitive functions.
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 dotlists) 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 ""
).
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.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
nchar
for counting the number of characters in character
vectors, lengths
for getting the length of every element
in a list.
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