[R] graph related question

[Jie]

Dear All,

I would like to draw a graph to illustrate the mapping between two vectors.
For instance,
a = c(2, 8, 5) ; mapped.a = c(8, 2, 5)

I would like to get some picture as
http://www.flickr.com/photos/96546690@N02/9569526581/

Basically, plot all points of a in a vertical line, and mapped.a in
another vertical line, finally link the same element by a arrow.
Thank you for any advice.

Best wishes
Jie