Matplotlib图例重复显示求助：循环调用sns.histplot致图例重复

使用Matplotlib和Seaborn读取CSV数据绘图时，通过for循环调用sns.histplot()绘制多列数据的直方图，出现了每个列的图例显示两次的问题。原代码如下：

import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
import numpy as np
import matplotlib

sns.set_style('darkgrid')
df = pd.read_csv('dm_office_sales.csv')
df['salary'] = df['salary'] * 3
df['sample salary'] = df['salary'] * 2
x = df['salary']
y = df['sales']
z = df['sample salary']

fig,ax = plt.subplots()
for i in [x,y,z]:
    sns.histplot(data = i, bins=50, ax=ax, palette = 'bright',alpha=0.3, label='{}'.format(i.name))

plt.legend(numpoints=1)
plt.suptitle('Sales/Salary Histogram')
plt.show()

问题原因 #

当传入的data是Pandas Series（即单独的列数据）时，sns.histplot()会自动基于Series的名称生成一个图例条目，同时手动设置的label参数又会添加一次相同的图例，最终导致重复显示。

解决方案 #

有两种简单的修复方式：

方法1：禁用histplot自动生成图例 #

在调用sns.histplot()时添加legend=False参数，只保留手动设置的label：

import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
import numpy as np
import matplotlib

sns.set_style('darkgrid')
df = pd.read_csv('dm_office_sales.csv')
df['salary'] = df['salary'] * 3
df['sample salary'] = df['salary'] * 2
x = df['salary']
y = df['sales']
z = df['sample salary']

fig,ax = plt.subplots()
for i in [x,y,z]:
    # 添加legend=False，关闭自动图例
    sns.histplot(data = i, bins=50, ax=ax, palette = 'bright',alpha=0.3, label='{}'.format(i.name), legend=False)

plt.legend(numpoints=1)
plt.suptitle('Sales/Salary Histogram')
plt.show()

方法2：直接传入DataFrame和列名（更规范的方式） #

循环列名而非单独的Series，通过x参数指定列名，这样histplot只会生成一次对应列名的图例：

import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
import numpy as np
import matplotlib

sns.set_style('darkgrid')
df = pd.read_csv('dm_office_sales.csv')
df['salary'] = df['salary'] * 3
df['sample salary'] = df['salary'] * 2

fig,ax = plt.subplots()
# 循环目标列名
for col in ['salary', 'sales', 'sample salary']:
    sns.histplot(data=df, x=col, bins=50, ax=ax, palette='bright', alpha=0.3, label=col)

plt.legend(numpoints=1)
plt.suptitle('Sales/Salary Histogram')
plt.show()

内容的提问来源于stack exchange，提问作者Raaghav Rammohan