自定义 Metrics
在 keras 中操作的均为 Tensor 对象，因此，需要定义操作 Tensor 的函数来操作所有输出结果，定义好函数之后，直接将其放在 model.compile 函数 metrics 中即可生效：
def precision(y_true, y_pred):
# Calculates the precision
true_positives = K.sum(K.round(K.clip(y_true * y_pred, 0, 1)))
predicted_positives = K.sum(K.round(K.clip(y_pred, 0, 1)))
precision = true_positives / (predicted_positives + K.epsilon())
return precision
def recall(y_true, y_pred):
# Calculates the recall
true_positives = K.sum(K.round(K.clip(y_true * y_pred, 0, 1)))
possible_positives = K.sum(K.round(K.clip(y_true, 0, 1)))
recall = true_positives / (possible_positives + K.epsilon())
return recall
def fbeta_score(y_true, y_pred, beta=1):
# Calculates the F score, the weighted harmonic mean of precision and recall.
if beta < 0:
raise ValueError('The lowest choosable beta is zero (only precision).')
# If there are no true positives, fix the F score at 0 like sklearn.
if K.sum(K.round(K.clip(y_true, 0, 1))) == 0:
return 0
p = precision(y_true, y_pred)
r = recall(y_true, y_pred)
bb = beta ** 2
fbeta_score = (1 + bb) * (p * r) / (bb * p + r + K.epsilon())
return fbeta_score
def fmeasure(y_true, y_pred):
# Calculates the f-measure, the harmonic mean of precision and recall.
return fbeta_score(y_true, y_pred, beta=1)
使用方法如下：
model.compile(
optimizer=Adam(),
loss='binary_crossentropy',
metrics = ['accuracy', fmeasure, recall, precision])
