Matplotlib绘制斜率图如何不修改yticks避免文本重叠并加百分比标注

问题1：解决左右文本标注重叠（不修改yticks） #

按如下调整即可解决重叠问题：

• 修正原有代码ylim设置错误，将范围匹配为yticks对应的3000~46000，避免高值数据标签被压缩重叠
• 扩大x轴范围至(-0.2,4.2)，给左右两侧标注预留更多展示空间
• 适当降低标注字号从14调整为12，减少单标签占用面积
  若仍有轻微重叠，可对相邻的y值接近的标签手动添加1000~2000的y轴偏移量错开位置。

问题2：添加摆动百分比标注到线段上方 #

将df2转为字典做映射匹配对应政党，在绘制每根线段时，取线段中点坐标添加百分比标注即可，可搭配白色半透明背景框提升可读性，颜色和线段涨跌色保持一致。

import matplotlib.pyplot as plt
import matplotlib.lines as mlines
import numpy as np
import pandas as pd

# 原始数据
df={'continent': {0: 'BJP', 1: 'INC', 2: 'BSP'},
 '1952': {0: 10650, 1: 30047, 2: 36828},
 '1957': {0: 42369, 1: 4482, 2: 4069}}
df = pd.DataFrame(df)

# 摆动数据
df2={'continent': {0: 'BJP', 1: 'INC', 2: 'BSP'},
 'Swing': {0: 31.9, 1: 9.9, 2: -42.5}}
df2 = pd.DataFrame(df2)
swing_map = df2.set_index('continent')['Swing'].to_dict()

klass = ['red' if (y1-y2) < 0 else 'green' for y1, y2 in zip(df['1952'], df['1957'])]

def newline(p1, p2, color='black'):
    ax = plt.gca()
    l = mlines.Line2D([p1[0],p2[0]], [p1[1],p2[1]], color='red' if p1[1]-p2[1] > 0 else 'green', marker='o', markersize=6)
    ax.add_line(l)
    return l

fig, ax = plt.subplots(1,1,figsize=(7,7), dpi= 80)

# Vertical Lines
ax.vlines(x=1, ymin=3500, ymax=45000, color='black', alpha=0.7, linewidth=1, linestyles='dotted')
ax.vlines(x=3, ymin=3500, ymax=45000, color='black', alpha=0.7, linewidth=1, linestyles='dotted')

# Points
ax.scatter(y=df['1952'], x=np.repeat(1, df.shape[0]), s=10, color='black', alpha=0.7)
ax.scatter(y=df['1957'], x=np.repeat(3, df.shape[0]), s=10, color='black', alpha=0.7)

# Line Segments and Annotation
for p1, p2, c in zip(df['1952'], df['1957'], df['continent']):
    newline([1,p1], [3,p2])
    # 左右标注调整字号
    ax.text(1-0.05, p1, c + ', ' + str(round(p1)), horizontalalignment='right', verticalalignment='center', fontdict={'size':12})
    ax.text(3+0.05, p2, c + ', ' + str(round(p2)), horizontalalignment='left', verticalalignment='center', fontdict={'size':12})
    # 添加摆动百分比标注
    swing_val = swing_map[c]
    mid_x = 2
    mid_y = (p1 + p2) / 2
    text_color = 'green' if swing_val > 0 else 'red'
    ax.text(mid_x, mid_y + 1500, f'{swing_val}%', ha='center', va='center', 
            color=text_color, fontsize=13, weight='bold',
            bbox=dict(facecolor='white', alpha=0.8, edgecolor='none', pad=2))

# 'Before' and 'After' Annotations
ax.text(1-0.05, 23000, 'BEFORE', horizontalalignment='right', verticalalignment='center', fontdict={'size':18, 'weight':700})
ax.text(3+0.05, 23000, 'AFTER', horizontalalignment='left', verticalalignment='center', fontdict={'size':18, 'weight':700})

# Decoration
ax.set_title("Vote Swing", fontdict={'size':22})
# 调整xlim和ylim
ax.set(xlim=(-0.2,4.2), ylim=(3000, 46000), ylabel='Votes')
ax.set_xticks([1,3])
ax.set_xticklabels(["2012", "2017"])
plt.yticks(np.arange(3500, 45000, 2000), fontsize=12)

# Lighten borders
plt.gca().spines["top"].set_alpha(.0)
plt.gca().spines["bottom"].set_alpha(.0)
plt.gca().spines["right"].set_alpha(.0)
plt.gca().spines["left"].set_alpha(.0)
plt.show()

内容的提问来源于stack exchange，提问作者DSR