Add subplot to existing figure?

Question

I'm trying to get to grips with matplotlib. I am having difficulty understanding how to add subplots when the grid shape already exists.

So for example if I create a figure with a 2*2 grid of subplots, how can I add a 5th or 6th. i.e. how can I change the geometry to accomodate another subplot. If I do this:

x = np.linspace(0, 2 * np.pi, 400)
y = np.sin(x ** 2)
f, ((ax1, ax2), (ax3, ax4)) = plt.subplots(2, 2, sharex=True, sharey=True, facecolor='red', \
dpi = 100, edgecolor = 'red', linewidth = 5.0, frameon = True)
ax1.plot(x, y)
ax1.set_title('Sharing x per column, y per row')
ax2.scatter(x, y)
ax3.scatter(x, 2 * y ** 2 - 1, color='r')
ax4.plot(x, 2 * y ** 2 - 1, color='r')

and then I want to add another subplot below:

f.add_subplot(3, 2, 5)

Then the new subplot overlaps with the fourth one, when I want it positioned below obviously. Do I need to change the geometry? If so, how? Or is it just a position thing?

More generally what is going on with the **kwargs with subplot? If anyone can help me work out how to start using those, that would also be very handy.

Answer 1

I think your intuition that you should change the geometry of the plot layout is correct. You are starting off by specifying a (2,2) geometry which is 2 rows and 2 columns, so naturally adding a 5th plot by conventional means can cause some issues. There are various ways to work around this, but one of the simpler solutions is just to give yourself a bigger subplot grid by using a third row of plots--using a (3,2) geometry as in my example below:

%pylab inline
import numpy as np
x = np.linspace(0, 2 * np.pi, 400)
y = np.sin(x ** 2)
#probably easiest to add a third row of plots (3,2) at this stage:
f, ((ax1, ax2), (ax3, ax4),(ax5,ax6)) = plt.subplots(3, 2, sharex=True, sharey=True,    facecolor='red', \
dpi = 100, edgecolor = 'red', linewidth = 5.0, frameon = True)
ax1.plot(x, y)
ax1.set_title('Sharing x per column, y per row')
ax2.scatter(x, y)
ax3.scatter(x, 2 * y ** 2 - 1, color='r')
ax4.plot(x, 2 * y ** 2 - 1, color='r')
#now the fifth plot shouldn't clobber one of the others:
ax5.plot(x,y**3,color='g')

If you want the fifth plot to take up the whole bottom row rather than having a blank 6th plot there you can use more advanced options like matplotlib.gridspec described in the gridspec documentation.