length(x) length(x) <- n
x is (or can be coerced to) a vector or list, length
returns the length of x.
Otherwise, length returns NA.
The second form above 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.
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