R: Length of an Object

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` | an integer: double values will be coerced to integer.

### 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 `NA`s (`nul` for raw vectors).

Both are primitive functions.

### Value

The default method currently returns an `integer` of length 1. Since this may change in the future and may differ for other methods, programmers should not rely on it.

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.

### Warning

Package authors have written methods that return a result of length other than one (Formula) and that return a vector type `double` (Matrix), even with non-integer values (sets).

### 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.

### 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

[Package base version 2.15.1 Index]