Matplotlib - ValueError: Illegal argument(s) to subplot

Question

I have 4 figures (y1,y2,y3,y4) that i want to plot on a common x axis (yr1,yr2,yr3,m1,m2,m3,m4,m5). In this code however i have kept axaxis as separate since i am trying to get the basics right first.

import matplotlib.pyplot as plt
import numpy as np

plt.figure(1)
xaxis = ['y1','y2','y3','m1','m2','m3', 'm4', 'm5']
y1 = np.array([.73,.74,.71,.75,.72,.75,.74,.74])
y2 = np.array([.82,.80,.77,.81,.72,.81,.77,.77])
y3 = np.array([.35,.36,.45,.43,.44,.45,.48,.45])
y4 = np.array([.49,.52,.59,.58,.61,.65,.61,.58])

plt.subplot(221)
plt.plot(xaxis,y1)
plt.subplot(222)
plt.plot(xaxis,y2)
plt.subplot(223)
plt.subplot(xaxis,y3)
plt.subplot(224)
plt.subplot(xaxis,y4)
plt.show()

Getting this error

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-23-dfe04cc8c6c4> in <module>
     14 plt.plot(xaxis,y2)
     15 plt.subplot(223)
---> 16 plt.subplot(xaxis,y3)
     17 plt.subplot(224)
     18 plt.subplot(xaxis,y4)

~\AppData\Local\Continuum\anaconda3\lib\site-packages\matplotlib\pyplot.py in subplot(*args, **kwargs)
   1074 
   1075     fig = gcf()
-> 1076     a = fig.add_subplot(*args, **kwargs)
   1077     bbox = a.bbox
   1078     byebye = []

~\AppData\Local\Continuum\anaconda3\lib\site-packages\matplotlib\figure.py in add_subplot(self, *args, **kwargs)
   1412                     self._axstack.remove(ax)
   1413 
-> 1414             a = subplot_class_factory(projection_class)(self, *args, **kwargs)
   1415 
   1416         return self._add_axes_internal(key, a)

~\AppData\Local\Continuum\anaconda3\lib\site-packages\matplotlib\axes\_subplots.py in __init__(self, fig, *args, **kwargs)
     62                 # num - 1 for converting from MATLAB to python indexing
     63         else:
---> 64             raise ValueError(f'Illegal argument(s) to subplot: {args}')
     65 
     66         self.update_params()

ValueError: Illegal argument(s) to subplot: (['y1', 'y2', 'y3', 'm1', 'm2', 'm3', 'm4', 'm5'], array([0.35, 0.36, 0.45, 0.43, 0.44, 0.45, 0.48, 0.45]))

Please help understand the issue here !

Bernardo Trindade · Accepted Answer · 2020-06-28 05:05:05Z

2

Reusing Sahith Kurapati's code just to provide a cleaner solution. This way you can share axes and only configure line and chart styles once if they're all supposed to have the same style.

import matplotlib.pyplot as plt
import numpy as np

plt.figure(1)
xaxis = ['y1','y2','y3','m1','m2','m3', 'm4', 'm5']
yy = np.array([[.73,.74,.71,.75,.72,.75,.74,.74],
              [.82,.80,.77,.81,.72,.81,.77,.77],
              [.35,.36,.45,.43,.44,.45,.48,.45],
              [.49,.52,.59,.58,.61,.65,.61,.58]])

fig, axes = plt.subplots(2, 2)
for y, ax in zip(yy, axes.ravel()):
    ax.plot(y)

plt.show()

answered Jun 28, 2020 at 5:05

Bernardo Trindade

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Comments

Sahith Kurapati · Accepted Answer · 2020-06-28 04:42:55Z

1

Small mistake. You have put plt.subplot instead of plt.plot. This should work now:

import matplotlib.pyplot as plt
import numpy as np

plt.figure(1)
xaxis = ['y1','y2','y3','m1','m2','m3', 'm4', 'm5']
y1 = np.array([.73,.74,.71,.75,.72,.75,.74,.74])
y2 = np.array([.82,.80,.77,.81,.72,.81,.77,.77])
y3 = np.array([.35,.36,.45,.43,.44,.45,.48,.45])
y4 = np.array([.49,.52,.59,.58,.61,.65,.61,.58])

plt.subplot(221)
plt.plot(xaxis,y1)
plt.subplot(222)
plt.plot(xaxis,y2)
plt.subplot(223)
plt.plot(xaxis,y3)
plt.subplot(224)
plt.plot(xaxis,y4)
plt.show()

Hope this helps :)

answered Jun 28, 2020 at 4:42

Sahith Kurapati

1,74513 silver badges15 bronze badges

Comments

Hamidreza · Accepted Answer · 2020-06-28 04:50:49Z

1

Try this:

fig, ax = plt.subplots(4, 1,sharex=True,gridspec_kw= {'height_ratios':[3,1,1,1]})
ax[0].plot(xais,y1)
ax[1].plot(xais,y1)
ax[2].plot(xais,y1)
ax[3].plot(xais,y1)

for 4 figures stacked on top of each other with shared x-axis.

for 2x2:

fig, ax = plt.subplots(2,2)
ax[0,0].plot(xaxis,y1)
ax[0,1].plot(xaxis,y1)
ax[1,0].plot(xaxis,y1)
ax[1,1].plot(xaxis,y1)

and then plt.show() to see results.

Look here for more: For more here is an example

answered Jun 28, 2020 at 4:50

Hamidreza

264 bronze badges

3 Comments

Gupta Over a year ago

Thanks a ton @user3850153 ! what are fig and ax. Looks like ax represent different graphs on the 2 x 2 plot for e.g. used ax[0,0].set_title('Fig 1') but what is "fig". How do we use it

Hamidreza Over a year ago

fig represents your whole figure. If you have another fig (running this command again) two windows will open. ax is an array of plots inside the figure. It could also be used like this: fig, ((ax1, ax2), (ax3, ax4)) = plt.subplot(2, 2) matplotlib.org/3.2.2/api/_as_gen/… matplotlib.org/3.2.2/api/_as_gen/…

Gupta Over a year ago

Thanks, This clarifies

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