Overplot seaborn regplot and swarmplot

Question

I would like to overplot a swarmplot and regplot in seaborn, so that I can have a y=x line through my swarmplot.

Here is my code:

import matplotlib.pyplot as plt
import seaborn as sns
    
sns.regplot(y=y, x=x, marker=' ', color='k')
sns.swarmplot(x=x_data, y=y_data)

I don't get any errors when I plot, but the regplot never shows on the plot. How can I fix this?

EDIT: My regplot and swarmplot don't overplot and instead, plot in the same frame but separated by some unspecified y amount. If I flip them so regplot is above the call to swarmplot, regplot doesn't show up at all.

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

df = pd.DataFrame({"x":x_data,"y":y_data} )

sns.regplot(y="y", x="x", data= df, color='k', scatter_kws={"alpha" : 0.0})
sns.swarmplot(y="y", x="x", data= df)

SECOND EDIT: The double axis solution from below works beautifully!

Answer 1

In principle the approach of plotting a swarmplot and a regplot simulatneously works fine.

The problem here is that you set an empty marker (marker = " "). This destroys the regplot, such that it's not shown. Apparently this is only an issue when plotting several things to the same graph; plotting a single regplot with empty marker works fine.

The solution would be not to specify the marker argument, but instead set the markers invisible by using the scatter_kws argument: scatter_kws={"alpha" : 0.0}.

Here is a complete example:

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

## generate some data
n=19; m=9
y_data = []
for i in range(m):
    a = (np.random.poisson(lam=0.99-float(i)/m,size=n)+i*.9+np.random.rand(1)*2)
    a+=(np.random.rand(n)-0.5)*2
    y_data.append(a*m)
y_data = np.array(y_data).flatten()
x_data = np.floor(np.sort(np.random.rand(n*m))*m)
## put them into dataframe
df = pd.DataFrame({"x":x_data,"y":y_data} )

## plotting
sns.regplot(y="y", x="x", data= df, color='k', scatter_kws={"alpha" : 0.0})
sns.swarmplot(x="x", y="y", data= df)

plt.show()

---

Concerning the edited part of the question:
Since swarmplot is a categorical plot, the axis in the plot still goes from -0.5 to 8.5 and not as the labels suggest from 10 to 18. A possible workaround is to use two axes and twiny.

fig, ax = plt.subplots()
ax2 = ax.twiny()
sns.swarmplot(x="x", y="y", data= df, ax=ax)
sns.regplot(y="y", x="x", data= df, color='k', scatter_kws={"alpha" : 0.0},  ax=ax2)
ax2.grid(False) #remove grid as it overlays the other plot