如何在Python中的组条形图的每个条上绘制多条水平线？

Question

I am trying to draw multiple horizontal lines on each bar of a group bar chart, that looks like this:

By multiple horizontal lines on a bar, I mean lines that are drawn at different Y-axis levels. For example, I would like to draw 1 horizontal line on Bar 3, Bar 4, and Bar 5 — all corresponding to the 300 Y-axis value; 1 horizontal line on Bar 5 corresponding to the 600 Y-axis value; 1 horizontal line on Bar 5 corresponding to the 900 Y-axis value.

Answer 1

One way to do it would be like this:

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

fig_dims = (11, 8)
fig, ax = plt.subplots(figsize=fig_dims)

df = pd.DataFrame({'Group': ['Group 1', 'Group 2',
                             'Group 1', 'Group 2',
                             'Group 1', 'Group 2',
                             'Group 1', 'Group 2',
                             'Group 1', 'Group 2'],
                   'Bars': ['Bar 1', 'Bar 1',
                            'Bar 2', 'Bar 2',
                            'Bar 3', 'Bar 3',
                            'Bar 4', 'Bar 4',
                            'Bar 5', 'Bar 5'],
                   'Size': [300, 300,
                            300, 300,
                            600, 600,
                            600, 600,
                            1200, 1200]})

lines_1 = pd.DataFrame({'Values': [0,  0,
                                   300,  300,
                                   300,  300,
                                   300,  300,
                                   300,  300]})
lines_2 = pd.DataFrame({'Values': [0,    0,
                                   0,    0,
                                   600,  600,
                                   600,  600,
                                   600,  600]})
lines_3 = pd.DataFrame({'Values': [0,    0,
                                   0,    0,
                                   0,    0,
                                   0,    0,
                                   900,  900]})

sns.barplot(x='Group', y='Size', hue='Bars', data=df,
            palette=['silver', 'cornflowerblue', 'royalblue', 'gold', 'darkgoldenrod'],
            ax=ax, edgecolor='black', linewidth=0.4)

plt.title('Group bar chart plot with horizontal lines drawn on each bar')
plt.ylabel('Dataset size')
y = np.array([0, 1200])
ticks = np.arange(y.min(), y.max()+10, 300.0)
plt.yticks(ticks)
ax.legend(loc='center left', bbox_to_anchor=(1, 0.5))

horizontal_lines = [lines_1, lines_2, lines_3]
for lines in horizontal_lines:
    for ix, a in enumerate(ax.patches):
        x_start = a.get_x()
        width = a.get_width()
        ax.plot([x_start, x_start + width], 2 * [lines.loc[ix, 'Values']], '-', c='black', linewidth=0.4)
plt.show()

which returns exactly what you've asked for