"""
======================================================
Effect of the shrinkage factor in random over-sampling
======================================================

This example shows the effect of the shrinkage factor used to generate the
smoothed bootstrap using the
:class:`~imblearn.over_sampling.RandomOverSampler`.
"""

# Authors: Guillaume Lemaitre <g.lemaitre58@gmail.com>
# License: MIT

# %%
print(__doc__)

import seaborn as sns

sns.set_context("poster")

# %%
# First, we will generate a toy classification dataset with only few samples.
# The ratio between the classes will be imbalanced.
from collections import Counter

from sklearn.datasets import make_classification

X, y = make_classification(
    n_samples=100,
    n_features=2,
    n_redundant=0,
    weights=[0.1, 0.9],
    random_state=0,
)
Counter(y)


# %%
import matplotlib.pyplot as plt

fig, ax = plt.subplots(figsize=(7, 7))
scatter = plt.scatter(X[:, 0], X[:, 1], c=y, alpha=0.4)
class_legend = ax.legend(*scatter.legend_elements(), loc="lower left", title="Classes")
ax.add_artist(class_legend)
ax.set_xlabel("Feature #1")
_ = ax.set_ylabel("Feature #2")
plt.tight_layout()

# %%
# Now, we will use a :class:`~imblearn.over_sampling.RandomOverSampler` to
# generate a bootstrap for the minority class with as many samples as in the
# majority class.
from imblearn.over_sampling import RandomOverSampler

sampler = RandomOverSampler(random_state=0)
X_res, y_res = sampler.fit_resample(X, y)
Counter(y_res)

# %%
fig, ax = plt.subplots(figsize=(7, 7))
scatter = plt.scatter(X_res[:, 0], X_res[:, 1], c=y_res, alpha=0.4)
class_legend = ax.legend(*scatter.legend_elements(), loc="lower left", title="Classes")
ax.add_artist(class_legend)
ax.set_xlabel("Feature #1")
_ = ax.set_ylabel("Feature #2")
plt.tight_layout()
# %%
# We observe that the minority samples are less transparent than the samples
# from the majority class. Indeed, it is due to the fact that these samples
# of the minority class are repeated during the bootstrap generation.
#
# We can set `shrinkage` to a floating value to add a small perturbation to the
# samples created and therefore create a smoothed bootstrap.
sampler = RandomOverSampler(shrinkage=1, random_state=0)
X_res, y_res = sampler.fit_resample(X, y)
Counter(y_res)

# %%
fig, ax = plt.subplots(figsize=(7, 7))
scatter = plt.scatter(X_res[:, 0], X_res[:, 1], c=y_res, alpha=0.4)
class_legend = ax.legend(*scatter.legend_elements(), loc="lower left", title="Classes")
ax.add_artist(class_legend)
ax.set_xlabel("Feature #1")
_ = ax.set_ylabel("Feature #2")
plt.tight_layout()

# %%
# In this case, we see that the samples in the minority class are not
# overlapping anymore due to the added noise.
#
# The parameter `shrinkage` allows to add more or less perturbation. Let's
# add more perturbation when generating the smoothed bootstrap.
sampler = RandomOverSampler(shrinkage=3, random_state=0)
X_res, y_res = sampler.fit_resample(X, y)
Counter(y_res)

# %%
fig, ax = plt.subplots(figsize=(7, 7))
scatter = plt.scatter(X_res[:, 0], X_res[:, 1], c=y_res, alpha=0.4)
class_legend = ax.legend(*scatter.legend_elements(), loc="lower left", title="Classes")
ax.add_artist(class_legend)
ax.set_xlabel("Feature #1")
_ = ax.set_ylabel("Feature #2")
plt.tight_layout()

# %%
# Increasing the value of `shrinkage` will disperse the new samples. Forcing
# the shrinkage to 0 will be equivalent to generating a normal bootstrap.
sampler = RandomOverSampler(shrinkage=0, random_state=0)
X_res, y_res = sampler.fit_resample(X, y)
Counter(y_res)

# %%
fig, ax = plt.subplots(figsize=(7, 7))
scatter = plt.scatter(X_res[:, 0], X_res[:, 1], c=y_res, alpha=0.4)
class_legend = ax.legend(*scatter.legend_elements(), loc="lower left", title="Classes")
ax.add_artist(class_legend)
ax.set_xlabel("Feature #1")
_ = ax.set_ylabel("Feature #2")
plt.tight_layout()

# %%
# Therefore, the `shrinkage` is handy to manually tune the dispersion of the
# new samples.