Seaborn列向stripplot报错ValueError：min()参数为空序列

问题重现 #

尝试用Seaborn绘制DataFrame列数据，代码如下：

#Plot CoV Vals per patient
#make df
data = {'Patient_ID': patient_list,
        'Manual Reader 1': intraCoV_kate_dict.values(),
        'Manual Reader 2': intraCoV_selene_dict.values(),
        'Automatic bg selection': intraCoV_homog_dict.values(),
       }
  
# Create DataFrame
df_plot_intra = pd.DataFrame(data)
print(df_plot_intra)
print(df_plot_intra.drop("Patient_ID", axis=1))

#plot with seaborn
sns.stripplot(data=df_plot_intra.drop("Patient_ID", axis=1), color = "Set2")

处理后的DataFrame：

Manual Reader 1     Manual Reader 2 Automatic bg selection
0    512121.7703226448   41915.74655761683      18103.86823163034
1    62971.19555431088  30371.248398078853     293949.27579836844
2    186444.3934911384  124438.71031050631     237108.97954526436
3    20464.24914545304  10433.799042052842      8920.798190557956
4    270549.4280501692    488004.964203974     114649.76948070318
5    553194.5961811391   752083.7511653332     46893.265540308035
6   1135634.3045041235   78546.71945962348      79877.27650659776
7    81995.44945779811    71576.4734166673     28025.684730116525
8    58135.01545385555   82652.93203094913     10399.192011960262
9    44931.50850748612  41390.559493600194     119254.46795220574
10  469287.15919308254   29877.27650659776      758667.5483106133
11  35321.755595259376   4413.871028266582      2630.377217394228
12   82658.52800267116   36445.10419234513     1266.6083717539414
13  117421.76949639994  514727.90414553485      71753.88248988726
14    651960.843691586  516501.42951649544      8733.196282802484

运行后触发错误：

ValueError                                Traceback (most recent call last)
Input In [102], in <cell line: 14>()
     12 print(df_plot_intra.drop("Patient_ID", axis=1))
     13 #plot with seaborn
---> 14 sns.stripplot(data=df_plot_intra.drop("Patient_ID", axis=1), color = "Set2")

File ~\anaconda3\envs\hids3\lib\site-packages\seaborn\_decorators.py:46, in _deprecate_positional_args.<locals>.inner_f(*args, **kwargs)
     36     warnings.warn(
     37         "Pass the following variable{} as {}keyword arg{}: {}. "
     38         "From version 0.12, the only valid positional argument "
   (...)
     43         FutureWarning
     44     )
     45 kwargs.update({k: arg for k, arg in zip(sig.parameters, args)})
---> 46 return f(**kwargs)

File ~\anaconda3\envs\hids3\lib\site-packages\seaborn\categorical.py:2807, in stripplot(x, y, hue, data, order, hue_order, jitter, dodge, orient, color, palette, size, edgecolor, linewidth, ax, **kwargs)
   2804     msg = "The `split` parameter has been renamed to `dodge`."
   2805     warnings.warn(msg, UserWarning)
-> 2807 plotter = _StripPlotter(x, y, hue, data, order, hue_order,
   2808                         jitter, dodge, orient, color, palette)
   2809 if ax is None:
   2810     ax = plt.gca()

File ~\anaconda3\envs\hids3\lib\site-packages\seaborn\categorical.py:1100, in _StripPlotter.__init__(self, x, y, hue, data, order, hue_order, jitter, dodge, orient, color, palette)
   1098 """Initialize the plotter."""
   1099 self.establish_variables(x, y, hue, data, orient, order, hue_order)
-> 1100 self.establish_colors(color, palette, 1)
   1102 # Set object attributes
   1103 self.dodge = dodge

File ~\anaconda3\envs\hids3\lib\site-packages\seaborn\categorical.py:319, in _CategoricalPlotter.establish_colors(self, color, palette, saturation)
    317 # Determine the gray color to use for the lines framing the plot
    318 light_vals = [colorsys.rgb_to_hls(*c)[1] for c in rgb_colors]
---> 319 lum = min(light_vals) * .6
    320 gray = mpl.colors.rgb2hex((lum, lum, lum))
    322 # Assign object attributes

ValueError: min() arg is an empty sequence

问题原因 #

错误根源是参数使用混淆：Set2是Seaborn的调色板（palette）名称，用于给不同类别分配一组颜色，但你把它传给了color参数——这个参数是用来指定单个统一颜色的，Seaborn无法将调色板名称解析为有效颜色，导致生成的颜色列表为空，进而触发min() arg is an empty sequence错误。

解决方案 #

把color="Set2"替换为palette="Set2"，让Seaborn正确识别调色板：

# 修正后的绘图代码
sns.stripplot(data=df_plot_intra.drop("Patient_ID", axis=1), palette="Set2")

如果想给所有数据点设置同一个颜色，才使用color参数，比如：

# 所有点用蓝色
sns.stripplot(data=df_plot_intra.drop("Patient_ID", axis=1), color="blue")

内容的提问来源于stack exchange，提问作者gmut