python pyplot : how to organize the layout?

Question

Looking at matplotlib documentation, I found this example:

http://matplotlib.org/users/tight_layout_guide.html

import matplotlib.pyplot as plt

def example_plot(ax,pid, fontsize=12):
    ax.plot([1, 2])
    ax.locator_params(nbins=3)
    ax.set_xlabel('x-label', fontsize=fontsize)
    ax.set_ylabel('y-label', fontsize=fontsize)
    ax.set_title('Title'+str(pid), fontsize=fontsize)

plt.close('all')
fig = plt.figure()

ax1 = plt.subplot(221)
ax2 = plt.subplot(223)
ax4 = plt.subplot(122)

example_plot(ax1,1)
example_plot(ax2,2)
example_plot(ax4,4)

plt.tight_layout()

plt.show()

which produce a 2 columns layout, on the left a column with two rows, and on the right a column with 1 row. This seems to match what the API of subplot is saying: http://matplotlib.org/api/pyplot_api.html

subplot(211) produces a subaxes in a figure which represents the top plot (i.e. the first) in a 2 row by 1 column notional grid (no grid actually exists, but conceptually this is how the returned subplot has been positioned).

I am now trying to add a row to the column of the left (for a total of 3 rows). From my understanding, that should do it:

import matplotlib.pyplot as plt

def example_plot(ax,pid, fontsize=12):
    ax.plot([1, 2])
    ax.locator_params(nbins=3)
    ax.set_xlabel('x-label', fontsize=fontsize)
    ax.set_ylabel('y-label', fontsize=fontsize)
    ax.set_title('Title'+str(pid), fontsize=fontsize)

plt.close('all')
fig = plt.figure()

ax1 = plt.subplot(321) # changed "2" by "3"
ax2 = plt.subplot(323) # changed "2" by "3"
ax3 = plt.subplot(324) # line added
ax4 = plt.subplot(122)

example_plot(ax1,1)
example_plot(ax2,2)
example_plot(ax3,3) # line added
example_plot(ax4,4)

plt.tight_layout()

plt.show()

There is something I must be doing wrong, because this display the right layout, but the third plot of the first column does not show up ....

Psirus · Accepted Answer · 2014-07-03 06:40:35Z

2

When you do a 3 by 2 subplot grid, the plots in the left column are numbered 1, 3 and 5. Change the line to ax3 = plt.subplot(325) and it should work.

answered Jul 3, 2014 at 6:40

Psirus

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2 Comments

Vince Over a year ago

Thanks ... just to make sure I understand why, it's because the number 4 is for the "imaginary" (rowspanned) plot on the right column ?

Psirus Over a year ago

Correct. You number the row first, in this case 1, 2; 3, 4; and 5, 6.

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