Matplotlib:将右轴的原点与特定的左轴值对齐 [英] Matplotlib: align origin of right axis with specific left axis value

问题描述

在Matplotlib中绘制多个y轴时，是否有一种方法可以指定如何将右轴的原点(和/或某些ytick标签)与左轴的特定值对齐?

When plotting several y axis in Matplotlib, is there a way to specify how to align the origin (and/or some ytick labels) of the right axis with a specific value of the left axis?

这是我的问题:我想绘制两组数据及其差异(基本上，我正在尝试重现

Here is my problem: I would like to plot two set of data as well as their difference (basically, I am trying to reproduce this kind of graph).

我可以复制它，但是我必须手动调整右轴的ylim，以使原点与我想要的左轴的值对齐.

I can reproduce it, but I have to manually adjust the ylim of the right axis so that the origin is aligned with the value I want from the left axis.

我在下面给出了我使用的代码的简化版本的示例.如您所见，我必须手动调整右轴的比例以对齐右轴和正方形的原点.

I putted below an example of a simplified version of the code I use. As you can see, I have to manually adjust scale of the right axis to align the origin of the right axis as well as the square.

import numpy as np
import scipy as sp
import matplotlib.pyplot as plt

grp1 = np.array([1.202, 1.477, 1.223, 1.284, 1.701, 1.724, 1.099,
                1.242, 1.099, 1.217, 1.291, 1.305, 1.333, 1.246])
grp2 = np.array([1.802, 2.399, 2.559, 2.286, 2.460, 2.511, 2.296,
                1.975])

fig = plt.figure(figsize=(6, 6))
ax = fig.add_axes([0.17, 0.13, 0.6, 0.7])

# remove top and right spines and turn ticks off if no spine
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
ax.spines['bottom'].set_color('none')
ax.xaxis.set_ticks_position('none')
ax.yaxis.set_ticks_position('left')
# postition of tick out
ax.tick_params(axis='both', direction='out', width=3, length=7,
        labelsize=24, pad=8)
ax.spines['left'].set_linewidth(3)

# plot groups vs random numbers to create dot plot
ax.plot(np.random.normal(1, 0.05, grp2.size), grp2, 'ok', markersize=10)
ax.plot(np.random.normal(2, 0.05, grp1.size), grp1, 'ok', markersize=10)
ax.errorbar(1, np.mean(grp2), fmt='_r', markersize=50,
        markeredgewidth=3)
ax.errorbar(2, np.mean(grp1), fmt='_r', markersize=50,
        markeredgewidth=3)


ax.set_xlim((0.5, 3.5))
ax.set_ylim((0, 2.7))

# create right axis
ax2 = fig.add_axes(ax.get_position(), sharex=ax, frameon=False)
ax2.spines['left'].set_color('none')
ax2.spines['top'].set_color('none')
ax2.spines['bottom'].set_color('none')
ax2.xaxis.set_ticks_position('none')
ax2.yaxis.set_ticks_position('right')
# postition of tick out
ax2.tick_params(axis='both', direction='out', width=3, length=7,
        labelsize=24, pad=8)
ax2.spines['right'].set_linewidth(3)
ax2.set_xticks([1, 2, 3])
ax2.set_xticklabels(('gr2', 'gr1', 'D'))
ax2.hlines(0, 0.5, 3.5, linestyle='dotted')
#ax2.hlines((np.mean(adult)-np.mean(nrvm)), 0, 3.5, linestyle='dotted')

ax2.plot(3, (np.mean(grp1)-np.mean(grp2)), 'sk', markersize=12)

# manual adjustment so the origin is aligned width left group2
ax2.set_ylim((-2.3, 0.42))
ax2.set_xlim((0.5, 3.5))

plt.show()

推荐答案

您可以创建一个小函数来计算 ax2 的对齐方式:

You can make a little function that calculates the alignment of ax2:

def align_yaxis(ax1, v1, ax2, v2):
    """adjust ax2 ylimit so that v2 in ax2 is aligned to v1 in ax1"""
    _, y1 = ax1.transData.transform((0, v1))
    _, y2 = ax2.transData.transform((0, v2))
    inv = ax2.transData.inverted()
    _, dy = inv.transform((0, 0)) - inv.transform((0, y1-y2))
    miny, maxy = ax2.get_ylim()
    ax2.set_ylim(miny+dy, maxy+dy)

通过使用align_yaxis()，您可以快速对齐轴:

by using align_yaxis(), you can align the axes quickly:

#...... your code

# adjustment so the origin is aligned width left group2
ax2.set_ylim((0, 2.7))
align_yaxis(ax, np.mean(grp2), ax2, 0)
plt.show()

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