matplotlib barh：如何在两组条之间制作视觉间隙？

Question

I have some sorted data of which I only show the highest and lowest values in a figure. This is a minimal version of what currently I have:

import matplotlib.pyplot as plt

# some dummy data (real data contains about 250 entries)
x_data = list(range(98, 72, -1))
labels = list('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
ranks = list(range(1, 27))

fig, ax = plt.subplots()

# plot 3 highest entries
bars_top = ax.barh(labels[:3], x_data[:3])
# plot 3 lowest entries
bars_bottom = ax.barh(labels[-3:], x_data[-3:])

ax.invert_yaxis()

# print values and ranks
for bar, value, rank in zip(bars_top + bars_bottom,
                            x_data[:3] + x_data[-3:],
                            ranks[:3] + ranks[-3:]):
    y_pos = bar.get_y() + 0.5
    ax.text(value - 4, y_pos, value, ha='right')
    ax.text(4, y_pos, f'$rank:\ {rank}$')

ax.set_title('Comparison of Top 3 and Bottom 3')
plt.show()

Result:

I'd like to make an additional gap to this figure to make it more visually clear that the majority of data is in fact not displayed in this plot. For example, something very simple like the following would be sufficient:

Is this possible in matplotlib?

Answer 1

Here is a flexible approach that just plots a dummy bar in-between. The yaxis-transform together with the dummy bar's position is used to plot 3 black dots.

If multiple separations are needed, they all need a different dummy label, for example repeating the space character.

import matplotlib.pyplot as plt
import numpy as np

# some dummy data (real data contains about 250 entries)
x_data = list(range(98, 72, -1))
labels = list('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
ranks = list(range(1, 27))

fig, ax = plt.subplots()

# plot 3 highest entries
bars_top = ax.barh(labels[:3], x_data[:3])
# dummy bar inbetween
dummy_bar = ax.barh(" ", 0, color='none')
# plot 3 lowest entries
bars_bottom = ax.barh(labels[-3:], x_data[-3:])

ax.invert_yaxis()

# print values and ranks
for bar, value, rank in zip(bars_top + bars_bottom,
                            x_data[:3] + x_data[-3:],
                            ranks[:3] + ranks[-3:]):
    y_pos = bar.get_y() + 0.5
    ax.text(value - 4, y_pos, value, ha='right')
    ax.text(4, y_pos, f'$rank:\ {rank}$')

# add three dots using the dummy bar's position
ax.scatter([0.05] * 3, dummy_bar[0].get_y() + np.linspace(0, dummy_bar[0].get_height(), 3),
           marker='o', s=5, color='black', transform=ax.get_yaxis_transform())

ax.set_title('Comparison of Top 3 and Bottom 3')
ax.tick_params(axis='y', length=0) # hide the tick marks
ax.margins(y=0.02) # less empty space at top and bottom
plt.show()

Answer 2

The following function,

def top_bottom(x, l, n, ax=None, gap=1):
    from matplotlib.pyplot import gca

    if n <= 0 : raise ValueError('No. of top/bottom values must be positive') 
    if n > len(x) : raise ValueError('No. of top/bottom values should be not greater than data length')
    if n+n > len(x):
        print('Warning: no. of top/bottom values is larger than one'
              ' half of data length, OVERLAPPING')
    if gap < 0 : print('Warning: some bar will be overlapped')
        
    ax = ax if ax else gca()
    
    top_x = x[:+n]
    bot_x = x[-n:]
    top_y = list(range(n+n, n, -1))
    bot_y = list(range(n-gap, -gap, -1))
    top_l = l[:+n] # A B C
    bot_l = l[-n:] # X Y Z

    top_bars = ax.barh(top_y, top_x)
    bot_bars = ax.barh(bot_y, bot_x)

    ax.set_yticks(top_y+bot_y)
    ax.set_yticklabels(top_l+bot_l)

    return top_bars, bot_bars

when invoked with your data and n=4 , gap=4

bars_top, bars_bottom = top_bottom(x_data, labels, 4, gap=4)

produces

Later, you'll be able to customize the appearance of the bars as you like using the Artists returned by the function.