如何为Matplotlib误差棒图的每个标记设置不同颜色？

问题场景 #

原本可以通过以下代码生成误差棒图：

import matplotlib.pyplot as plt
import pandas as pd

data = {'x': [194.33, 281.0, 317.5, 118.66666666666667, 143.0], 
        'y': [292.83, 284.45, 302.47, 178.8, 165.81], 
        'error':[191.83094965214667, 188.15999999999997, 170.51999999999998, 35.951147099609756, 27.439999999999998],
        'color': ['yellow','red','red','yellow','red']}

df = pd.DataFrame(data)
fig, ax = plt.subplots()
ax.errorbar(x=df['x'], y=df['y'], yerr=df['error'], fmt='o', ecolor='black', elinewidth=1, capsize=5, c='blue')

但尝试用c=df['color']给每个点设置对应颜色时，触发错误：

ValueError: RGBA sequence should have length 3 or 4

解决方法 #

方法1：用scatter单独绘制彩色点

errorbar的c参数不支持直接传入字符串颜色列表，可先绘制无点的误差棒，再用scatter绘制带对应颜色的点：

import matplotlib.pyplot as plt
import pandas as pd

data = {'x': [194.33, 281.0, 317.5, 118.66666666666667, 143.0], 
        'y': [292.83, 284.45, 302.47, 178.8, 165.81], 
        'error':[191.83094965214667, 188.15999999999997, 170.51999999999998, 35.951147099609756, 27.439999999999998],
        'color': ['yellow','red','red','yellow','red']}

df = pd.DataFrame(data)
fig, ax = plt.subplots()

# 仅绘制误差棒，不显示点
ax.errorbar(x=df['x'], y=df['y'], yerr=df['error'], fmt='none', ecolor='black', elinewidth=1, capsize=5)
# 用scatter绘制对应颜色的点
ax.scatter(df['x'], df['y'], c=df['color'], marker='o')

plt.show()

方法2：遍历数据逐个绘制误差棒

适合数据量较小的场景，遍历每行数据，单独设置每个误差棒的点颜色：

import matplotlib.pyplot as plt
import pandas as pd

data = {'x': [194.33, 281.0, 317.5, 118.66666666666667, 143.0], 
        'y': [292.83, 284.45, 302.47, 178.8, 165.81], 
        'error':[191.83094965214667, 188.15999999999997, 170.51999999999998, 35.951147099609756, 27.439999999999998],
        'color': ['yellow','red','red','yellow','red']}

df = pd.DataFrame(data)
fig, ax = plt.subplots()

# 遍历每行数据，单独绘制误差棒和点
for _, row in df.iterrows():
    ax.errorbar(x=row['x'], y=row['y'], yerr=row['error'], fmt='o', ecolor='black', elinewidth=1, capsize=5, c=row['color'])

plt.show()

原因说明 #

Matplotlib的errorbar函数c参数仅接受单一颜色值或RGBA数值数组，不支持直接传入字符串颜色列表；而scatter函数的c参数支持字符串颜色列表，因此第一种方法效率更高。

内容的提问来源于stack exchange，提问作者Bera