如何使用 keras 对一种热编码使用分类焦点损失？

Question

我正在研究癫痫发作预测。我有不平衡的数据集，我想通过使用焦点损失来使其平衡。我有 2 类 one-hot 编码向量。我找到了下面的焦点损失代码，但我不知道如何在 model.fit_generator 之前将 y_pred 用于焦点损失代码。

y_pred 是模型的输出。那么在拟合模型之前如何在焦点损失代码中使用它呢？？

局部损失代码：

def categorical_focal_loss(gamma=2.0, alpha=0.25):
    """
    Implementation of Focal Loss from the paper in multiclass classification
    Formula:
        loss = -alpha*((1-p)^gamma)*log(p)
    Parameters:
        alpha -- the same as wighting factor in balanced cross entropy
        gamma -- focusing parameter for modulating factor (1-p)
    Default value:
        gamma -- 2.0 as mentioned in the paper
        alpha -- 0.25 as mentioned in the paper
    """
    def focal_loss(y_true, y_pred):
        # Define epsilon so that the backpropagation will not result in NaN
        # for 0 divisor case
        epsilon = K.epsilon()
        # Add the epsilon to prediction value
        #y_pred = y_pred + epsilon
        # Clip the prediction value
        y_pred = K.clip(y_pred, epsilon, 1.0-epsilon)
        # Calculate cross entropy
        cross_entropy = -y_true*K.log(y_pred)
        # Calculate weight that consists of  modulating factor and weighting factor
        weight = alpha * y_true * K.pow((1-y_pred), gamma)
        # Calculate focal loss
        loss = weight * cross_entropy
        # Sum the losses in mini_batch
        loss = K.sum(loss, axis=1)
        return loss
    
    return focal_loss

我的代码：

history=model.fit_generator(generate_arrays_for_training(indexPat, train_data, start=0,end=100)
validation_data=generate_arrays_for_training(indexPat, test_data, start=0,end=100)
steps_per_epoch=int((len(train_data)/2)), 
                                validation_steps=int((len(test_data)/2)),
                                verbose=2,epochs=65, max_queue_size=2, shuffle=True)
preictPrediction=model.predict_generator(generate_arrays_for_predict(indexPat, filesPath_data), max_queue_size=4, steps=len(filesPath_data))
y_pred1=np.argmax(preictPrediction,axis=1)
y_pred=list(y_pred1)

Answer 1

来自评论区造福社区

This is not specific to focal loss, all keras loss functions take y_true and y_pred, you do not need to worry where those parameters are coming from, they are fed by keras automatically.

如何使用 keras 对一种热编码使用分类焦点损失？

How to use categorial focal loss for one hot encoding with keras?

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