我怎样才能在 python 中的 x 轴上有两个不同的线性刻度？

Question

有没有一种方法可以在 python 图中的 x 轴上设置两个不同的比例？

我有以下代码：

import numpy as np
from matplotlib import pyplot as plt
import pandas as pd

data=pd.read_csv(file, names=['Wavenumber', 'Intensity'])

fig=plt.figure()
ax=fig.add_subplot(1,1,1)
ax.plot(data['Wavenumber'], data['Intensity'])
ax.invert_xaxis()
ax.set_xticks([4000,3000,2000,1600,1200,800,400])
plt.show()

这给出：

但我希望刻度线之间的间距相等，因此以 1000 为步长从 4000 线性缩放到 2000，然后以 400 为步长从 2000 线性缩放到 400。这应该如下所示：

Answer 1

在 matplotlib 中创建自定义比例可以quite an effort. As you only need two different linear scales, it is easier to use a workaround consisting of joining two subplots together. With many data points located near the boundary between the two scales (as in your case), the jump from one to the other will not cause any irregular space between the ticks around the boundary if you were to show many tick marks (contrary to here). All you need is to find the data point closest to the boundary 无缝连接两个子图，如下例所示：

import numpy as np               # v 1.19.2
import pandas as pd              # v 1.1.3
import matplotlib.pyplot as plt  # v 3.3.2

# Create sample dataset
rng = np.random.default_rng(seed=1)
x = np.linspace(4000, 400, num=50)
y = 1 - rng.exponential(scale=0.1, size=x.size)
df = pd.DataFrame(dict(Wavenumber=x, Intensity=y))

# Select data for each subplot by using a boundary point
x_boundary = min(df['Wavenumber'], key=lambda x: abs(x-2000))
df1 = df[df['Wavenumber'] >= x_boundary]
df2 = df[df['Wavenumber'] <= x_boundary]

# Select x-axis ticks for each subplot
ticks = np.array([4000, 3000, 2000, 1600, 1200, 800, 400])
tk1 = ticks[ticks >= x_boundary]
tk2 = ticks[ticks <= x_boundary]

# Create figure with 2 Axes side-by-side with no space in between
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(10, 5), sharey=True,
                               gridspec_kw=dict(wspace=0))

# Loop through both Axes to plot data, adjust x-axis limits and remove boundary spines
for ax, data, spine, tk in zip((ax1, ax2), (df1, df2), ('right','left'), (tk1, tk2)):
    data.plot(x='Wavenumber', xlabel='', ax=ax, legend=None)
    ax.set_xlim(data['Wavenumber'].iloc[[0,-1]])
    ax.spines[spine].set_visible(False)
    ax.set_xticks(tk)

# Additional formatting
ax2.tick_params(axis='y', length=0)
ax1.set_xlabel('Wavenumber', x=1, labelpad=10, size=12)
ax1.set_ylabel('Intensity', labelpad=10, size=12)
fig.suptitle('Plot with two linear x-axis scales joined together', size=16, y=0.95);

我怎样才能在 python 中的 x 轴上有两个不同的线性刻度？

How can I have two different linear scales in x-axis in python?

python

matplotlib

scale

xticks