title: Sorting a list of coordinates based on x-axis
body: <p>Well, I am new to R.  what I want is plot a graph, I have the data for my x-axis and y-axis. Now I have a list of coordinates, I want to plot them in the graph, but before that I want to sort the the list of coordinates according to the data for x-axis only, and how can I do that? Thanks </p>