Setting flier (outlier) style in Seaborn boxplot is ignored

Question

Using Seaborn, I can create boxplots of multiple columns of one pandas DataFrame on the same figure. I would like to apply a custom style to the fliers (outliers), e.g. setting the marker symbol, color and marker size.

The API documentation on seaborn.boxplot, however, only provides an argument fliersize which lets me control the size of the fliers but not the color and symbol.

Since Seaborn uses matplotlib for plotting, I thought I could provide a matplotlib styling dictionary to the boxplot function like so:

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

# create a dataframe
df = pd.DataFrame({'column_a': [3, 6, 200, 100, 7], 'column_b': [1, 8, 4, 150, 290], 'column_c': [6, 7, 20, 80, 275]})

# set figure size
sns.set(rc={"figure.figsize": (14, 6)})

# define outlier properties
flierprops = dict(marker='o', markersize=5)

# create boxplot
ax = sns.boxplot(df, vert=False, showmeans=True, flierprops=flierprops)
plt.show()

Result:

According to the provided dictionary, I would expect a large red circle representing the flyer of column_c but instead, the standard settings are still used.

This thread describes a similar problem when matplotlib is used directly - however, from the discussion I guessed that this should be fixed meanwhile when using recent versions of matplotlib.

I tried this with an iPython notebook (iPython 3.10), matplotlib 1.4.3 and seaborn 0.5.1.

Answer 1

Seaborn's boxplot code ignores your flierprops argument and overwrites it with its own before passing arguments to Matplotlib's. Matplotlib's boxplot also returns all the flier objects as part of its return value, so you could modify this after running boxplot, but Seaborn doesn't return this.

The overwriting of flierprops (and sym) seems like a bug, so I'll see if I can fix it: see this issue. Meanwhile, you may want to consider using matplotlib's boxplot instead. Looking at seaborn's code may be useful (boxplot is in distributions.py).

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Update: there is now a pull request that fixes this (flierprops and other *props, but not sym)

Answer 2

flierprops = dict(marker='o', markerfacecolor='None', markersize=10,  markeredgecolor='black')
sns.boxplot(y=df.Column,orient="v",flierprops=flierprops)