DecisionBoundaryDisplay.from_estimator only displays up to 7 distinct colours #32866
Description
Describe the bug
I was trying to use DecisionBoundaryDisplay.from_estimator to display different regions classified by NuSVC:
My expectation was to find 11, but by visually counting, I was only able to find 10.
Also, some colours were obviously duplicated in this figure.
This is how it actually should look like:
Proposed fix
I guess that this will be fixed at some point by matplotlib/matplotlib@0eadaf0. However, this fix is not yet available in the stable versions of matplotlib.
Manually changing the "default"/hard-wired value here fixes the problem.
The best fix, thus, is probably for scikit-learn to specify the levels parameter on its own here:
That line should look something like this:
self.surface_ = plot_func(self.xx0, self.xx1, self.response, <levels>, **kwargs)where <levels> is replaced by the appropriate amount of levels.
The case when self.response.ndim == 3 may also be affected, but I have not yet tried out that one
Steps/Code to Reproduce
import numpy as np
from sklearn.inspection import DecisionBoundaryDisplay
from sklearn.svm import NuSVC
import matplotlib.pyplot as plt
# List of some 11 distinct points
pts = np.array([[-1, -1], [-2, -1], [1, 1], [2, 1],
[2, 2], [3, 2], [3, 3], [4, 3],
[4, 4], [5, 4], [5, 5]])
svc = NuSVC(nu=0.1)
svc.fit(pts, [1,2,3,4,5,6,7,8,9,10,11])
DecisionBoundaryDisplay.from_estimator(
svc,
pts,
response_method="predict",
cmap="gist_rainbow"
)
plt.show()Expected Results
Actual Results
Versions
System:
python: 3.12.7 | packaged by Anaconda, Inc. | (main, Oct 4 2024, 13:27:36) [GCC 11.2.0]
executable: /home/nico/miniconda3/envs/pca-assessment/bin/python
machine: Linux-6.14.0-36-generic-x86_64-with-glibc2.39
Python dependencies:
sklearn: 1.7.2
pip: 24.3.1
setuptools: 72.1.0
numpy: 2.3.3
scipy: 1.16.2
Cython: None
pandas: 2.3.2
matplotlib: 3.10.6
joblib: 1.4.2
threadpoolctl: 3.5.0
Built with OpenMP: True
threadpoolctl info:
user_api: blas
internal_api: openblas
num_threads: 16
prefix: libscipy_openblas
filepath: /home/nico/miniconda3/envs/pca-assessment/lib/python3.12/site-packages/numpy.libs/libscipy_openblas64_-8fb3d286.so
version: 0.3.30
threading_layer: pthreads
architecture: Haswell
user_api: blas
internal_api: mkl
num_threads: 12
prefix: libmkl_rt
filepath: /home/nico/miniconda3/envs/pca-assessment/lib/libmkl_rt.so.2
version: 2025.0-Product
threading_layer: gnu
user_api: openmp
internal_api: openmp
num_threads: 16
prefix: libgomp
filepath: /home/nico/miniconda3/envs/pca-assessment/lib/libgomp.so.1.0.0
version: None