Unknow error with sns.violinplot when selecting only one ‘x’ attribute

[songyuc]

Hi, guys,
I am learning using seaborn today, and met an unknow error with sns.violinplot when selecting only one ‘x’ attribute as,

import seaborn as sns
sns.set_theme(style="whitegrid")

# Load the example tips dataset
tips = sns.load_dataset("tips")

# Draw a nested violinplot and split the violins for easier comparison
sns.violinplot(data=tips[tips["day"]=="Fri"], x="day", y="total_bill", hue="smoker",
               inner="quart", linewidth=1,split=True,
               palette={"Yes": "b", "No": ".85"})
sns.despine(left=True)

And here was the error message,

C:\Users\46630\anaconda3\envs\conda-general\lib\site-packages\seaborn\categorical.py:1261: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison if j and any(self.plot_hues[0] == hue_level): --------------------------------------------------------------------------- TypeError Traceback (most recent call last) Input In [5], in () 5 tips = sns.load_dataset("tips") 7 # Draw a nested violinplot and split the violins for easier comparison ----> 8 sns.violinplot(data=tips[tips["day"]=="Fri"], x="day", y="total_bill", hue="smoker", 9 inner="quart", linewidth=1,split=True, 10 palette={"Yes": "b", "No": ".85"}) 11 sns.despine(left=True)

File ~\anaconda3\envs\conda-general\lib\site-packages\seaborn\categorical.py:2312, in violinplot(data, x, y, hue, order, hue_order, bw, cut, scale, scale_hue, gridsize, width, inner, split, dodge, orient, linewidth, color, palette, saturation, ax, **kwargs)
2309 if ax is None:
2310 ax = plt.gca()
-> 2312 plotter.plot(ax)
2313 return ax

File ~\anaconda3\envs\conda-general\lib\site-packages\seaborn\categorical.py:1419, in _ViolinPlotter.plot(self, ax)
1417 def plot(self, ax):
1418 """Make the violin plot."""
-> 1419 self.draw_violins(ax)
1420 self.annotate_axes(ax)
1421 if self.orient == "h":

File ~\anaconda3\envs\conda-general\lib\site-packages\seaborn\categorical.py:1261, in _ViolinPlotter.draw_violins(self, ax)
1255 self.draw_stick_lines(ax, violin_data,
1256 support, density, i,
1257 ["left", "right"][j])
1259 # The box and point interior plots are drawn for
1260 # all data at the group level, so we just do that once
-> 1261 if j and any(self.plot_hues[0] == hue_level):
1262 continue
1264 # Get the whole vector for this group level

TypeError: 'bool' object is not iterable

Could please tell me how to fix it?

Your answer and guide will be appreciated!

[mwaskom]

I think this is a subtle bug in seaborn that specifically happens with (A) split violins and (B) categorical grouping variable. If you disable the split you can see that it is still trying to draw the other levels (this is by design, there's just a bug where it doesn't handle empty data in those levels properly):

What I would do is not worry about selecting rows from the dataframe and instead just ask for a specific level using order:

sns.violinplot(
    data=tips,
    x="day", y="total_bill", hue="smoker",
    order=["Fri"],  # <--- Add this
    inner="quart", linewidth=1, split=True,
    palette={"Yes": "b", "No": ".85"}
)