length                 package: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.

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).

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. (Should the length
     exceed the maximum representable integer, it is returned as 'NA'.)

     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.

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

