Reverse the Order of a Vector or List
DESCRIPTION:
Returns an object with the same length as x but with the elements or components in the reverse order.
USAGE: 
rev(x)
REQUIRED ARGUMENTS:
x:
an object with length, usually a vector.
Missing values (NA) are allowed.
VALUE:
object like x but with the order reversed (the last value in x is the first value in the result).
SEE ALSO:
c , list , rep , sort .
EXAMPLES: 
rev(sort(y))    # sort y in descending order


rev(list(a=1:2, b=5:6)) # same as list(b=5:6, a=1:2)