Plotting a line over several graphs

Question

I don\'t know how this thing is called, or even how to describe it, so the title may be a little bit misleading.

The first attached graph was created with pyplot.

Answer 1

[Update 03/2013] In newer revisions of matplotlib, there's ConnectionPatch that greatly simplifies this task. It's particularly useful whenever there are more than two subplots that need to be covered.

from matplotlib import pyplot as plt
from matplotlib.patches import ConnectionPatch
from numpy import arange, sin, cos

xx = arange(100)
cut = (xx > 0) & (xx % 17 == 0)
y1 = sin(xx)
y2 = (xx**2) % 2.0+cos(xx+0.5)

fig = plt.figure()
ax1 = fig.add_subplot(211)
ax1.plot(xx, y1, c="blue")
ax1.scatter(xx[cut], y1[cut], c="red")
ax2 = fig.add_subplot(212)
ax2.plot(xx, y2, c="green")
ax2.scatter(xx[cut], y2[cut], c="red")

for x in xx[cut]:
    con = ConnectionPatch(xyA=(x, -1.5), xyB=(x, 1.5),
        coordsA="data", coordsB="data", axesA=ax2, axesB=ax1,
        arrowstyle="-", linewidth=2, color="red")
    ax2.add_artist(con)

plt.draw()
fig.savefig('pic.png')