Merge subplots with shared x-axis

Question

I have two graphs to where both have the same x-axis, but with different y-axis scalings.

The plot with regular axes is the data with a trend line depicting a decay while the y semi-log scaling depicts the accuracy of the fit.

fig1 = plt.figure(figsize=(15,6))
ax1 = fig1.add_subplot(111)

# Plot of the decay model 
ax1.plot(FreqTime1,DecayCount1, '.', color='mediumaquamarine')

# Plot of the optimized fit
ax1.plot(x1, y1M, '-k', label='Fitting Function: $f(t) = %.3f e^{%.3f\t} \
         %+.3f$' % (aR1,kR1,bR1))

ax1.set_xlabel('Time (sec)')
ax1.set_ylabel('Count')
ax1.set_title('Run 1 of Cesium-137 Decay')

# Allows me to change scales
# ax1.set_yscale('log')
ax1.legend(bbox_to_anchor=(1.0, 1.0), prop={'size':15}, fancybox=True, shadow=True)

Now, i'm trying to figure out to implement both close together like the examples supplied by this link http://matplotlib.org/examples/pylab_examples/subplots_demo.html

In particular, this one

When looking at the code for the example, i'm a bit confused on how to implant 3 things:

1) Scaling the axes differently

2) Keeping the figure size the same for the exponential decay graph but having a the line graph have a smaller y size and same x size.

For example:

3) Keeping the label of the function to appear in just only the decay graph.

Any help would be most appreciated.

Tom Neiser · Accepted Answer · 2021-01-26 16:04:46Z

52

Look at the code and comments in it:

import matplotlib.pyplot as plt
import numpy as np
from matplotlib import gridspec

# Simple data to display in various forms
x = np.linspace(0, 2 * np.pi, 400)
y = np.sin(x ** 2)

fig = plt.figure()
# set height ratios for subplots
gs = gridspec.GridSpec(2, 1, height_ratios=[2, 1]) 

# the first subplot
ax0 = plt.subplot(gs[0])
# log scale for axis Y of the first subplot
ax0.set_yscale("log")
line0, = ax0.plot(x, y, color='r')

# the second subplot
# shared axis X
ax1 = plt.subplot(gs[1], sharex = ax0)
line1, = ax1.plot(x, y, color='b', linestyle='--')
plt.setp(ax0.get_xticklabels(), visible=False)
# remove last tick label for the second subplot
yticks = ax1.yaxis.get_major_ticks()
yticks[-1].label1.set_visible(False)

# put legend on first subplot
ax0.legend((line0, line1), ('red line', 'blue line'), loc='lower left')

# remove vertical gap between subplots
plt.subplots_adjust(hspace=.0)
plt.show()

edited Jan 26, 2021 at 16:04

Tom Neiser

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answered Jun 10, 2016 at 2:05

Serenity

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4 Comments

Yushan Over a year ago

@Serenity Great answer! But is it possible to have shared x axis if I use fig, axis = plt.subplots(nrows=4) to create my axis array?

Serenity Over a year ago

Yep, it is possible, why not?

Yushan Over a year ago

@Serenity Well, I think this is possible if using plt.plot() then I could specify sharex. But in Pandas I cannot get a touch to the underlying sharex, I have to make a new axis to pass for the DataFrame.plot(). That's why I like your answer!

normanius Over a year ago

Note that one can create the two axes in one call: fig, (ax0, ax1) = plt.subplots(2,1, sharex=True, gridspec_kw=dict(height_ratios=[2, 1]))

Aray Karjauv · Accepted Answer · 2020-06-19 22:21:06Z

13

Here is my solution:

import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 2 * np.pi, 400)
y = np.sin(x ** 2)

fig, (ax1,ax2) = plt.subplots(nrows=2, sharex=True, subplot_kw=dict(frameon=False)) # frameon=False removes frames

plt.subplots_adjust(hspace=.0)
ax1.grid()
ax2.grid()

ax1.plot(x, y, color='r')
ax2.plot(x, y, color='b', linestyle='--')

One more option is seaborn.FacetGrid but this requires Seaborn and Pandas libraries.

edited Jun 19, 2020 at 22:21

answered Feb 17, 2020 at 18:46

Aray Karjauv

2,9552 gold badges31 silver badges46 bronze badges

Comments

JohanC · Accepted Answer · 2021-11-19 01:04:35Z

Here are some adaptions to show how the code could work to add a combined legend when plotting a pandas dataframe. ax=ax0 can be used to plot on a given ax and ax0.get_legend_handles_labels() gets the information for the legend.

import matplotlib.pyplot as plt
import pandas as pd
import numpy as np

dates = pd.date_range('20210101', periods=100, freq='D')
df0 = pd.DataFrame({'x': np.random.normal(0.1, 1, 100).cumsum(),
                    'y': np.random.normal(0.3, 1, 100).cumsum()}, index=dates)
df1 = pd.DataFrame({'z': np.random.normal(0.2, 1, 100).cumsum()}, index=dates)

fig, (ax0, ax1) = plt.subplots(nrows=2, sharex=True, gridspec_kw={'height_ratios': [2, 1], 'hspace': 0})

df0.plot(ax=ax0, color=['dodgerblue', 'crimson'], legend=False)
df1.plot(ax=ax1, color='limegreen', legend=False)

# put legend on first subplot
handles0, labels0 = ax0.get_legend_handles_labels()
handles1, labels1 = ax1.get_legend_handles_labels()
ax0.legend(handles=handles0 + handles1, labels=labels0 + labels1)

# remove last tick label for the second subplot
yticks = ax1.get_yticklabels()
yticks[-1].set_visible(False)

plt.tight_layout()
plt.show()

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