如何在共享X、Y轴的Matplotlib双图中合并X、Y轴刻度

I see the issue here—when you call ax.set_xticks() twice in a row, the second call completely overwrites the first one, which is why only the ticks from your second dataset are showing up. The same goes for the Y-axis ticks. To fix this, you need to combine the tick values from both datasets first, then set them on the axis once.

Fixed Code #

import matplotlib.pyplot as plt
import matplotlib.dates as md
from datetime import datetime

# Dataset 1
v1 = datetime.fromisoformat("2022-10-15T23:45:51.159618277Z")
v2 = datetime.fromisoformat("2022-10-16T23:49:51.159618277Z")
v3 = datetime.fromisoformat("2022-10-17T22:25:46.638699435Z")
t_time_values1 = [v1, v2, v3]
datenums1 = md.date2num(t_time_values1)
y1 = [30, 15, 45]

# Dataset 2
v4 = datetime.fromisoformat("2022-10-15T05:45:51.159618277Z")
v5 = datetime.fromisoformat("2022-10-16T05:49:51.159618277Z")
v6 = datetime.fromisoformat("2022-10-17T02:25:46.638699435Z")
t_time_values2 = [v4, v5, v6]
datenums2 = md.date2num(t_time_values2)
y2 = [78, 25, 55]

# Plot lines
ax = plt.gca()
xfmt = md.DateFormatter('%Y-%m-%d %H:%M:%S.%f')
ax.xaxis.set_major_formatter(xfmt)

plt.plot(datenums1, y1, label="line 1")
plt.plot(datenums2, y2, label="line 2")

# Combine and sort X-axis ticks (dates are numerical, so sorting works)
combined_xticks = sorted(datenums1 + datenums2)
ax.set_xticks(combined_xticks)

# Combine and sort Y-axis ticks
combined_yticks = sorted(y1 + y2)
ax.set_yticks(combined_yticks)

# Rotate X-tick labels for readability (optional but recommended)
plt.xticks(rotation=45)

plt.legend()
plt.tight_layout()  # Adjust layout to prevent label cutoff
plt.show()

Key Changes Explained: #

• Combining Tick Values: Instead of setting ticks twice, we merge the tick lists from both datasets (datenums1 + datenums2 for X, y1 + y2 for Y) and sort them. This ensures all unique tick positions are included and ordered correctly.
• Avoid Overwriting: By calling ax.set_xticks() and ax.set_yticks() only once with the combined lists, we preserve all ticks from both plots.
• Readability Improvements: Added plt.xticks(rotation=45) and plt.tight_layout() to prevent long date labels from getting cut off.

Why Your Original Code Didn't Work: #

Matplotlib's set_xticks() replaces the existing tick array each time you call it. So when you ran ax.set_xticks(datenums1) followed by ax.set_xticks(datenums2), the first set of ticks was discarded entirely—only the second set remained. Merging the lists first fixes this by including all desired tick positions in one go.

内容的提问来源于stack exchange，提问作者User1751