How to generate separate violinplots for each class and group

Question

I have a pandas dataframe:

df = pd.DataFrame(np.random.randint(0,100,size=(100, 4)), columns=list('ABCD'))
df['Label'] = np.random.randint(0,2,size=100)

I would like to create a figure in python where x-axis shows the class labels ('Class 0' and 'Class 1') and for each class and for a pre-defined variable like 'B' the violin plot (with a box-plot inside) is created.

Answer 1

• You want to convert the dataframe to a long format with panda.DataFrame.melt and then plot with seaborn.violinplot or seaborn.catplot.
• pandas 1.3.0, seaborn 0.11.1, matplotlib 3.4.2

Import and DataFrame

import pandas as pd
import seaborn as sns

# sample data
df = pd.DataFrame(np.random.randint(0, 100, size=(100, 4)), columns=list('ABCD'))
df['Class'] = np.random.randint(0, 2, size=100)

# melt the dataframe to a long form
dfm = df.melt(id_vars='Class', var_name='Group')

# display(dfm.head())
   Class Group  value
0      1     A     12
1      1     A     43
2      0     A     58
3      1     A     49
4      1     A     47

Plotting

seaborn.violinplot

p = sns.violinplot(data=dfm, x='Group', y='value', hue='Class')
p.legend(title='Class', bbox_to_anchor=(1, 1), loc='upper left')

• With x='Group', hue='Class'

• With x='Class', hue='Group'

seaborn.catplot

• To easily plot separately for each group, use seaborn.catplot with kind='violin'

sns.catplot(kind='violin', data=dfm, x='Class', y='value', col='Group', col_wrap=2)

Answer 2

Using seaborn, it is pretty straightforward:

import seaborn as sns
...
sns.violinplot(x=df.Label, y=df.B)