I am merging two graphs and one has 23 data points, the other has 9. The
category axis will have 23 data points but the 9 points are spread out, i.e.
they may be at points 1, 3, 7, 15 etc of the 23-point scale. At the moment
the graph will only join points that are beside each other; how do I get them
to connect to the points that have spaces between them?