scikit-learn/examples/semi_supervised/plot_label_propagation_structure.py

"""
==============================================
Label Propagation learning a complex structure
==============================================

Example of LabelPropagation learning a complex internal structure
to demonstrate "manifold learning". The outer circle should be
labeled "red" and the inner circle "blue". Because both label groups
lie inside their own distinct shape, we can see that the labels
propagate correctly around the circle.

"""

# Authors: Clay Woolam <clay@woolam.org>
#          Andreas Mueller <amueller@ais.uni-bonn.de>
# License: BSD

# %%
# We generate a dataset with two concentric circles. In addition, a label
# is associated with each sample of the dataset that is: 0 (belonging to
# the outer circle), 1 (belonging to the inner circle), and -1 (unknown).
# Here, all labels but two are tagged as unknown.

import numpy as np
from sklearn.datasets import make_circles

n_samples = 200
X, y = make_circles(n_samples=n_samples, shuffle=False)
outer, inner = 0, 1
labels = np.full(n_samples, -1.0)
labels[0] = outer
labels[-1] = inner

# %%
# Plot raw data
import matplotlib.pyplot as plt

plt.figure(figsize=(4, 4))
plt.scatter(
    X[labels == outer, 0],
    X[labels == outer, 1],
    color="navy",
    marker="s",
    lw=0,
    label="outer labeled",
    s=10,
)
plt.scatter(
    X[labels == inner, 0],
    X[labels == inner, 1],
    color="c",
    marker="s",
    lw=0,
    label="inner labeled",
    s=10,
)
plt.scatter(
    X[labels == -1, 0],
    X[labels == -1, 1],
    color="darkorange",
    marker=".",
    label="unlabeled",
)
plt.legend(scatterpoints=1, shadow=False, loc="upper right")
plt.title("Raw data (2 classes=outer and inner)")

# %%
#
# The aim of :class:`~sklearn.semi_supervised.LabelSpreading` is to associate
# a label to sample where the label is initially unknown.
from sklearn.semi_supervised import LabelSpreading

label_spread = LabelSpreading(kernel="knn", alpha=0.8)
label_spread.fit(X, labels)

# %%
# Now, we can check which labels have been associated with each sample
# when the label was unknown.
output_labels = label_spread.transduction_
output_label_array = np.asarray(output_labels)
outer_numbers = np.where(output_label_array == outer)[0]
inner_numbers = np.where(output_label_array == inner)[0]

plt.figure(figsize=(4, 4))
plt.scatter(
    X[outer_numbers, 0],
    X[outer_numbers, 1],
    color="navy",
    marker="s",
    lw=0,
    s=10,
    label="outer learned",
)
plt.scatter(
    X[inner_numbers, 0],
    X[inner_numbers, 1],
    color="c",
    marker="s",
    lw=0,
    s=10,
    label="inner learned",
)
plt.legend(scatterpoints=1, shadow=False, loc="upper right")
plt.title("Labels learned with Label Spreading (KNN)")
plt.show()