pythonseabornfacet-gridrelplot

FacetGrid returned seaborn's relplot does not respect hue

I am encountering a problem in which seaborn's relplot function creates a FacetGrid that is different from creating the FacetGrid manually. I find this unintuitive and would like the relplot function to give me a FacetGrid that behaves similarly to the manually created one.

The issue is that when using the map function on the FacetGrid returned from relplot, it does not consider a specified hue anymore. Here is a minimal example that explains my point:

import numpy as np
import seaborn as sns
import pandas as pd

def foo(color=None, label=None, tag=None):
    print(tag, color, label)

x = np.random.randn(100)
df = pd.DataFrame({
    'x' : x,
    'y' : 2 * x,
    'row' : np.random.randn(x.shape[0]) > 0,
    'col' : np.random.randn(x.shape[0]) > 0,
    'hue' : np.random.randn(x.shape[0]) > 0,
})
g = sns.relplot(data = df, x = 'x', y = 'y', row='row', col='col', hue='hue')
g.map(foo, tag='relplot')

g2 = sns.FacetGrid(data = df, row = 'row', col = 'col', hue='hue')
g2.map(foo, tag='FacetGrid')

When calling the map function on the facet grid returned by relplot, it will only be called four times (once per row and column) but will not respect the fact that I also specified a hue. The output is:

relplot (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) None
relplot (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) None
relplot (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) None
relplot (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) None

If I map the same function to the FacetGrid that is manually created, it will result in the expected behaviour:

FacetGrid (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) False
FacetGrid (0.8666666666666667, 0.5176470588235295, 0.3215686274509804) True
FacetGrid (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) False
FacetGrid (0.8666666666666667, 0.5176470588235295, 0.3215686274509804) True
FacetGrid (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) False
FacetGrid (0.8666666666666667, 0.5176470588235295, 0.3215686274509804) True
FacetGrid (0.2980392156862745, 0.4470588235294118, 0.6901960784313725) False
FacetGrid (0.8666666666666667, 0.5176470588235295, 0.3215686274509804) True

Is there any explanation as to why that happens? Is there a way to change relplot's behaviour to match the expected one, i.e. to respect the hue parameter I set?

Solution

  • Is there any explanation as to why that happens?

    Yes, in relplot the hue logic is all handled within scatterplot, not by the FacetGrid.

    Is there a way to change relplot's behaviour to match the expected one?

    No, in this case you'll want to make your custom function handle the hue logic internally or start with FacetGrid directly.