I have 2 sets of depth point measurements, for example:

> a
  depth value
1     2     2
2     4     3
3     6     4
4     8     5
5    16    40
6    18    45
7    20    58

> b
  depth value
1    10    10
2    12    20
3    14    35

I want to show both groups in one figure plotted with depth and with different symbols as you can see here

plot(a$value, a$depth, type='b', col='green', pch=15)
points(b$value, b$depth, type='b', col='red', pch=14)

The plot seems okay, but the annoying part is that the green symbols are all connected (though I want connected lines also). I want connection only when one group has a continued data points at 2 m interval i.e. the symbols should be connected with a line from 2 to 8 m (green) and then group B symbols should be connected from 10-14 m (red) and again group A symbols should be connected (green), which means I do NOT want to see the connection between 8 m sample with the 16 m for group A.

An easy solution may be dividing the group A into two parts (say, A-shallow and A-deep) and then plotting A-shallow, B, and A-deep separately. But this is completely impractical because I have thousands of data points with hundreds of groups i.e. I have to produce many depth profiles. Therefore, there has to be a way to program so that dots are NOT connected beyond a prescribed frequency/depth interval (e.g. 2 m in this case) for a particular group of samples. Any idea?