Python matplotlib分组柱状图重叠问题求助

Hey there! Let's sort out why your grouped bars are overlapping—it's a common tiny logic tweak, no worries.

The Root Cause #

Your bar_width is too large for three bars per category. You set bar_width = 0.45, so three bars take up a total width of 3 * 0.45 = 1.35. But since each category (from np.arange(n_groups)) is spaced 1 unit apart, this means the third bar of one category spills into the next category's space, causing the overlap.

The Fix #

1. Reduce the bar width: Use a value that makes the total width per category less than 1. A solid choice is 0.3 (or 1/3 for exact spacing).
2. Adjust x-tick positions: Center the ticks under the middle of each three-bar group instead of the original position.

Here's your modified code with these changes highlighted:

import numpy as np
import matplotlib.pyplot as plt

# Assuming market, dmarket, pmarket are defined elsewhere with 3 elements each
n_groups = 3
credits = (market[0], market[1], market[2])
debits = (dmarket[0], dmarket[1], dmarket[2])
profits = (pmarket[0], pmarket[1], pmarket[2])

fig, ax = plt.subplots()
index = np.arange(n_groups)
# Reduced bar width to fit three bars per category
bar_width = 0.3
opacity = 0.4
error_config = {'ecolor': '0.3'}

rectsCredits = plt.bar(index, credits, bar_width, alpha=opacity, color='b', error_kw=error_config, label='Credit')
rectsDebits = plt.bar(index + bar_width, debits, bar_width, alpha=opacity, color='r', error_kw=error_config, label='Debit')
rectsProfits = plt.bar(index + 2*bar_width, profits, bar_width, alpha=opacity, color='g', error_kw=error_config, label='Profits')

# Adjusted tick position to center under the three-bar group
plt.xticks(index + bar_width, ('Tariff Market', 'Wholesale Market', 'Balancing Market'))
plt.legend()
plt.tight_layout()

def autolabel(rects):
    """ Attach a text label above each bar displaying its height """
    for rect in rects:
        height = rect.get_height()
        ax.text(rect.get_x() + rect.get_width() / 2., 1.01 * height, '%d' % int(height), ha='center', va='bottom')

autolabel(rectsCredits)
autolabel(rectsDebits)
autolabel(rectsProfits)

plt.show()

Why This Works #

• With bar_width = 0.3, three bars take up 0.9 units of space per category, leaving a small gap between groups for clarity.
• The plt.xticks(index + bar_width, ...) moves each tick to the middle of the three bars (since the first bar starts at index, the second at index+bar_width, third at index+2*bar_width—the center is exactly index+bar_width).

内容的提问来源于stack exchange，提问作者Jannik