如何使用 Keras 神經網絡分類器在 KFold 交叉驗證中為每個折疊繪制 ROC_AUC 曲線

Question

我真的需要在使用 Keras ANN 的 5 折交叉驗證中為每個折疊找到 ROC 圖。 我已經嘗試了以下鏈接中的代碼 [https://scikit-learn.org/stable/auto_examples/model_selection/plot_roc_crossval.html#sphx-glr-auto-examples-model-selection-plot-roc-crossval-py] [1] 當我使用 svm 分類器時，它工作得非常好，如下所示。 但是當我想使用包裝器來使用 Keras ANN 模型時，它會顯示錯誤。 我已經堅持了幾個月了。 任何人都可以幫我嗎？ 這是我的代碼：

# Load libraries
import numpy as np
from keras import models
from keras import layers
from keras.wrappers.scikit_learn import KerasClassifier
from sklearn.model_selection import cross_val_score
from sklearn.datasets import load_breast_cancer
from sklearn.model_selection import StratifiedKFold

X, y = load_breast_cancer(return_X_y=True)
# Create function returning a compiled network
def create_network():
    
    # Start neural network
    network = models.Sequential()

    # Add fully connected layer with a ReLU activation function
    network.add(layers.Dense(units=16, activation='relu', input_shape=(30,)))

    # Add fully connected layer with a ReLU activation function
    network.add(layers.Dense(units=16, activation='relu'))

    # Add fully connected layer with a sigmoid activation function
    network.add(layers.Dense(units=1, activation='sigmoid'))

    # Compile neural network
    network.compile(loss='binary_crossentropy', # Cross-entropy
                    optimizer='rmsprop', # Root Mean Square Propagation
                    metrics=['accuracy']) # Accuracy performance metric
    
    # Return compiled network
    return network

cv = StratifiedKFold(n_splits=5)
# Wrap Keras model so it can be used by scikit-learn
classifier = KerasClassifier(build_fn=create_network, 
                                 epochs=10, 
                                 batch_size=100, 
                                 verbose=2)
#Plotting the ROC curve
tprs = []
aucs = []
mean_fpr = np.linspace(0, 1, 100)

fig, ax = plt.subplots()
for i, (train, test) in enumerate(cv.split(X, y)):
    classifier.fit(X[train], y[train])
    viz = plot_roc_curve(classifier, X[test], y[test],
                         name='ROC fold {}'.format(i),
                         alpha=0.3, lw=1, ax=ax)
    interp_tpr = np.interp(mean_fpr, viz.fpr, viz.tpr)
    interp_tpr[0] = 0.0
    tprs.append(interp_tpr)
    aucs.append(viz.roc_auc)

ax.plot([0, 1], [0, 1], linestyle='--', lw=2, color='r',
        label='Chance', alpha=.8)

mean_tpr = np.mean(tprs, axis=0)
mean_tpr[-1] = 1.0
mean_auc = auc(mean_fpr, mean_tpr)
std_auc = np.std(aucs)
ax.plot(mean_fpr, mean_tpr, color='b',
        label=r'Mean ROC (AUC = %0.2f $\pm$ %0.2f)' % (mean_auc, std_auc),
        lw=2, alpha=.8)

std_tpr = np.std(tprs, axis=0)
tprs_upper = np.minimum(mean_tpr + std_tpr, 1)
tprs_lower = np.maximum(mean_tpr - std_tpr, 0)
ax.fill_between(mean_fpr, tprs_lower, tprs_upper, color='grey', alpha=.2,
                label=r'$\pm$ 1 std. dev.')

ax.set(xlim=[-0.05, 1.05], ylim=[-0.05, 1.05],
       title="Receiver operating characteristic example")
ax.legend(loc="lower right")
plt.show()

它顯示以下錯誤：

Epoch 1/10
5/5 - 0s - loss: 24.0817 - accuracy: 0.3714
Epoch 2/10
5/5 - 0s - loss: 2.7967 - accuracy: 0.5648
Epoch 3/10
5/5 - 0s - loss: 2.0594 - accuracy: 0.5363
Epoch 4/10
5/5 - 0s - loss: 2.4763 - accuracy: 0.5604
Epoch 5/10
5/5 - 0s - loss: 2.5489 - accuracy: 0.5121
Epoch 6/10
5/5 - 0s - loss: 2.0528 - accuracy: 0.6132
Epoch 7/10
5/5 - 0s - loss: 1.5593 - accuracy: 0.6088
Epoch 8/10
5/5 - 0s - loss: 2.0422 - accuracy: 0.5626
Epoch 9/10
5/5 - 0s - loss: 1.9191 - accuracy: 0.6242
Epoch 10/10
5/5 - 0s - loss: 1.9914 - accuracy: 0.5582
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-104-2d127e528fbe> in <module>()
      8     viz = plot_roc_curve(classifier, X[test], y[test],
      9                          name='ROC fold {}'.format(i),
---> 10                          alpha=0.3, lw=1, ax=ax)
     11     interp_tpr = np.interp(mean_fpr, viz.fpr, viz.tpr)
     12     interp_tpr[0] = 0.0

/usr/local/lib/python3.6/dist-packages/sklearn/metrics/_plot/roc_curve.py in plot_roc_curve(estimator, X, y, sample_weight, drop_intermediate, response_method, name, ax, **kwargs)
    170     )
    171     if not is_classifier(estimator):
--> 172         raise ValueError(classification_error)
    173 
    174     prediction_method = _check_classifer_response_method(estimator,

ValueError: KerasClassifier should be a binary classifier

Answer 1

這是這個包裝器庫中（可能）缺少的一個實現細節。

Sklearn 只是檢查估計器上是否存在名為_estimator_type的屬性並將其設置為字符串值classifier 。 您可以通過在 github 上查看 sklearn 的源代碼來了解這一點。

def is_classifier(estimator):
    """Return True if the given estimator is (probably) a classifier.
    Parameters
    ----------
    estimator : object
        Estimator object to test.
    Returns
    -------
    out : bool
        True if estimator is a classifier and False otherwise.
    """
    return getattr(estimator, "_estimator_type", None) == "classifier"

您需要做的就是手動將此屬性添加到分類器對象中。

classifier = KerasClassifier(build_fn=create_network, 
                                 epochs=10, 
                                 batch_size=100, 
                                 verbose=2)

classifier._estimator_type = "classifier"

我已經測試過它並且它有效。