混淆矩阵三类python

数据挖掘 Python 混淆矩阵
2021-09-17 00:25:41

我想计算:

True_Positive, False_Positive, False_Negative, True_Negative

为三个类别。我曾经有两个班级Cat Dog,这是我用来计算我的混淆矩阵的方式

y_pred 有猫或狗

y_true 有猫或狗

from sklearn.metrics import confusion_matrix
confusion_matrix_output =confusion_matrix(y_true, y_pred) 
True_Positive = confusion_matrix_output[0][0]
False_Positive = confusion_matrix_output[0][1]
False_Negative = confusion_matrix_output[1][0]
True_Negative = confusion_matrix_output[1][1]

现在我有三个班“猫”“狗”“兔子”

Y_pred has Cat Dog rabbit
y_true has Cat Dog rabbit

如何计算True_Positive, False_Positive, False_Negative, True_Negative

1个回答

多类混淆矩阵在文献中非常成熟;您可以自己轻松找到它。无论如何,Scikit-learn可以很容易地做到这一点:

from sklearn.metrics import confusion_matrix

y_true = ['Cat', 'Dog', 'Rabbit', 'Cat', 'Cat', 'Rabbit']
y_pred = ['Dog', 'Dog', 'Rabbit', 'Dog', 'Dog', 'Rabbit']

classes=['Cat', 'Dog', 'Rabbit']

confusion_matrix(y_true, y_pred, labels=['Cat', 'Dog', 'Rabbit'])

array([[0, 3, 0],
       [0, 1, 0],
       [0, 0, 2]])

您甚至可以使用以下函数很好地绘制它:

def plot_confusion_matrix(cm, classes,
                          normalize=False,
                          title='Confusion matrix',
                          cmap=plt.cm.Blues):
    """
    This function prints and plots the confusion matrix.
    Normalization can be applied by setting `normalize=True`.
    """
    import itertools
    if normalize:
        cm = cm.astype('float') / cm.sum(axis=1)[:, np.newaxis]
        print("Normalized confusion matrix")
    else:
        print('Confusion matrix, without normalization')

    print(cm)

    plt.imshow(cm, interpolation='nearest', cmap=cmap)
    plt.title(title)
    plt.colorbar()
    tick_marks = np.arange(len(classes))
    plt.xticks(tick_marks, classes, rotation=45)
    plt.yticks(tick_marks, classes)

    fmt = '.2f' if normalize else 'd'
    thresh = cm.max() / 2.
    for i, j in itertools.product(range(cm.shape[0]), range(cm.shape[1])):
        plt.text(j, i, format(cm[i, j], fmt),
                 horizontalalignment="center",
                 color="white" if cm[i, j] > thresh else "black")

    plt.ylabel('True label')
    plt.xlabel('Predicted label')
    plt.tight_layout()

像这样:

cnf_matrix = confusion_matrix(y_true, y_pred,labels=['Cat', 'Dog', 'Rabbit'])
np.set_printoptions(precision=2)

# Plot non-normalized confusion matrix
plt.figure()
plot_confusion_matrix(cnf_matrix, classes=['Cat', 'Dog', 'Rabbit'],
                      title='Confusion matrix, without normalization')

在此处输入图像描述

更多示例在这里这里