Multi-axis x with matplotlib python

Question

My aim is to get something that looks like the image below:

For the moment I've tried to build it like this:

import matplotlib.pyplot as plt
import numpy as np 

X = ['Class 1','Class 2','Class 3','Class 4', 'Class 5', 'Class 6', 'Class 7'] 

sE = ['-9,51', '-13,5', '0,193', '9,564', '23,13', '-0,252', '-0,442']
s = ['19,605', '28,388', '1,762', '-4,264', '-24,716', '-26,956', '0,382']
eE = ['-5,364', '-7,954', '-3,756', '-0,184', '1,883', '41,876', '-0,012']


X_axis = np.arange(len(X)) 

# plt.bar(X_axis, sE, color='red',width = 0.25, edgecolor='black') 
# plt.bar(X_axis+0.25, s, color='cyan',width = 0.25, edgecolor='black') 
# plt.bar(X_axis+0.5, eE, color='green',width = 0.25, edgecolor='black') 

#plt.hist([sE, s, eE], color = ['red', 'cyan', 'green'], edgecolor = 'black', histtype = 'bar')

#plt.xticks(X_axis, X) 
plt.xlabel("Classes")  
plt.title("Geographical STP A") 
plt.show() 

But we're a long way from achieving the desired result. I really have no idea how to do this, can you help me ?

Answer 1

To be able to plot, the strings should be converted to numeric.

Plots with multiple bars per X-value are much easier using the Pandas (or Seaborn) library which builds on matplotlib for plotting. Your data doesn't have data for histogram, you seem to want a bar plot.

Here is some code. Many customizations are possible.

import matplotlib.pyplot as plt
import pandas as pd

X = ['Class 1', 'Class 2', 'Class 3', 'Class 4', 'Class 5', 'Class 6', 'Class 7']

sE = ['-9,51', '-13,5', '0,193', '9,564', '23,13', '-0,252', '-0,442']
s = ['19,605', '28,388', '1,762', '-4,264', '-24,716', '-26,956', '0,382']
eE = ['-5,364', '-7,954', '-3,756', '-0,184', '1,883', '41,876', '-0,012']

# organize the data as a pandas dataframe
df = pd.DataFrame({'Class': X, 'sE': sE, 's': s, 'eE': eE})

# convert strings to numeric
df['sE'] = df['sE'].str.replace(',','.').astype(float)
df['s'] = df['s'].str.replace(',','.').astype(float)
df['eE'] = df['eE'].str.replace(',','.').astype(float)

ax = df.set_index('Class').plot(kind='bar')

ax.set_title("Geographical STP A")
ax.tick_params(axis='x', rotation=0)

plt.show()

Possible customizations could include:

ax = df.set_index('Class').plot(kind='bar', color=['crimson', 'limegreen', 'dodgerblue'])

ax.set_title("Geographical STP A")
ax.tick_params(axis='x', rotation=0, length=0)  # rotate tick labels horizontally, remove tick mark
ax.grid(True, axis='y')  # add a grid in the y direction
ax.set_xlabel('')  # remove superfluous x label
for dir in ['top', 'bottom', 'right']:
    ax.spines[dir].set_visible(False)  # remove the border around the plot

PS: The dataframe looks like:

Class	sE	s	eE
Class 1	-9.51	19.605	-5.364
Class 2	-13.5	28.388	-7.954
Class 3	0.193	1.762	-3.756
Class 4	9.564	-4.264	-0.184
Class 5	23.13	-24.716	1.883
Class 6	-0.252	-26.956	41.876
Class 7	-0.442	0.382	-0.012