Obtaining span of plotted points from seaborn swarmplot

Question

I have the following data:

import pandas as pd
import numpy as np

# Generate dummy data.
a = np.random.random(75)
b = np.random.random(75) - 0.6
c = np.random.random(75) + 0.75 

# Collate into a DataFrame
df = pd.DataFrame({'a': a, 'b': b, 'c': c}) 
df.columns = [list(['WT', 'MUT', 'WTxMUT']), list(['Parent', 'Parent', 'Offspring'])]
df.columns.names = ['Genotype', 'Status']
df_melt = pd.melt(df) 

and I plot it in seaborn using this code:

import seaborn as sb
sb.swarmplot(data = df_melt, x = "Status", y = "value", hue = "Genotype")

How do I get the x-span of each group? What is the range of the horizontal span of the swarmplot for the Parent group, for instance?

Answer 1

You can get the information from the collections which are created by swarmplot .

swarmplot actually returns the matplotlib Axes instance, and from there we can find the PathCollections that it creates. To get the positions, we can use .get_offsets() .

Here is your example, modified to find and print the swarm limits, and then use them to plot a box around the swarms.

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sb
from matplotlib.patches import Rectangle

# Generate dummy data.
a = np.random.random(75)
b = np.random.random(75) - 0.6
c = np.random.random(75) + 0.75 

# Collate into a DataFrame
df = pd.DataFrame({'a': a, 'b': b, 'c': c}) 
df.columns = [list(['WT', 'MUT', 'WTxMUT']), list(['Parent', 'Parent', 'Offspring'])]
df.columns.names = ['Genotype', 'Status']
df_melt = pd.melt(df) 

ax = sb.swarmplot(data = df_melt, x = "Status", y = "value", hue = "Genotype")

def getdatalim(coll):
    x,y = np.array(coll.get_offsets()).T
    try:
        print 'xmin={}, xmax={}, ymin={}, ymax={}'.format(
                x.min(), x.max(), y.min(), y.max())
        rect = Rectangle((x.min(),y.min()),x.ptp(),y.ptp(),edgecolor='k',facecolor='None',lw=3)
        ax.add_patch(rect)
    except ValueError:
        pass

getdatalim(ax.collections[0]) # "Parent"
getdatalim(ax.collections[1]) # "Offspring"

plt.show()

which prints:

xmin=-0.107313729132, xmax=0.10661092707, ymin=-0.598534246847, ymax=0.980441247759
xmin=0.942829146473, xmax=1.06105941656, ymin=0.761277608688, ymax=1.74729717464

And here's the figure: