绘制验证曲线

在这个例子中，我们检查了SMOTE的 k_neighbors参数的影响。在图中，你可以看到对于不同值的 SMOTE的k_neighbors参数，SMOTE-CART分类器的验证分数。

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

print(__doc__)

import seaborn as sns

sns.set_context("poster")


RANDOM_STATE = 42

首先，我们生成一个类别分布不平衡的数据集。

from sklearn.datasets import make_classification

X, y = make_classification(
    n_classes=2,
    class_sep=2,
    weights=[0.1, 0.9],
    n_informative=10,
    n_redundant=1,
    flip_y=0,
    n_features=20,
    n_clusters_per_class=4,
    n_samples=5000,
    random_state=RANDOM_STATE,
)

我们将使用一个过采样器 SMOTE，然后使用 DecisionTreeClassifier。目标将是搜索哪个 k_neighbors 参数最适合我们生成的数据集。

from sklearn.tree import DecisionTreeClassifier

from imblearn.over_sampling import SMOTE
from imblearn.pipeline import make_pipeline

model = make_pipeline(
    SMOTE(random_state=RANDOM_STATE), DecisionTreeClassifier(random_state=RANDOM_STATE)
)

我们可以使用validation_curve来检查 改变参数k_neighbors的影响。在这种情况下，我们需要 使用一个分数来评估交叉验证期间的泛化分数。

from sklearn.metrics import cohen_kappa_score, make_scorer
from sklearn.model_selection import validation_curve

scorer = make_scorer(cohen_kappa_score)
param_range = range(1, 11)
train_scores, test_scores = validation_curve(
    model,
    X,
    y,
    param_name="smote__k_neighbors",
    param_range=param_range,
    cv=3,
    scoring=scorer,
)

train_scores_mean = train_scores.mean(axis=1)
train_scores_std = train_scores.std(axis=1)
test_scores_mean = test_scores.mean(axis=1)
test_scores_std = test_scores.std(axis=1)

我们现在可以绘制我们尝试的不同参数值的交叉验证结果。

import matplotlib.pyplot as plt

fig, ax = plt.subplots(figsize=(7, 7))
ax.plot(param_range, test_scores_mean, label="SMOTE")
ax.fill_between(
    param_range,
    test_scores_mean + test_scores_std,
    test_scores_mean - test_scores_std,
    alpha=0.2,
)
idx_max = test_scores_mean.argmax()
ax.scatter(
    param_range[idx_max],
    test_scores_mean[idx_max],
    label=r"Cohen Kappa: ${:.2f}\pm{:.2f}$".format(
        test_scores_mean[idx_max], test_scores_std[idx_max]
    ),
)

fig.suptitle("Validation Curve with SMOTE-CART")
ax.set_xlabel("Number of neighbors")
ax.set_ylabel("Cohen's kappa")

# make nice plotting
sns.despine(ax=ax, offset=10)
ax.set_xlim([1, 10])
ax.set_ylim([0.4, 0.8])
ax.legend(loc="lower right", fontsize=16)
plt.tight_layout()
plt.show()

预计内存使用量： 199 MB