我正在尝试将二进制日志丢失应用于我创建的Naive Bayes ML模型。我生成了分类预测数据集(yNew)和概率数据集(probabilityYes),但无法在对数损失函数中成功运行它们。
简单的sklearn.metrics函数给出单个对数丢失结果-不确定如何解释这一点
from sklearn.metrics import log_loss
ll = log_loss(yNew, probabilityYes, eps=1e-15)
print(ll)
.0819....
更复杂的函数为每个否返回2.55的值,为每个是返回2.50的值(总共90列)-再次,不知道如何解释这一点
def logloss(yNew,probabilityYes):
epsilon = 1e-15
probabilityYes = sp.maximum(epsilon, probabilityYes)
probabilityYes = sp.minimum(1-epsilon, probabilityYes)
#compute logloss function (vectorised)
ll = sum(yNew*sp.log(probabilityYes) +
sp.subtract(1,yNew)*sp.log(sp.subtract(1,probabilityYes)))
ll = ll * -1.0/len(yNew)
return ll
print(logloss(yNew,probabilityYes))
2.55352047 2.55352047 2.50358354 2.55352047 2.50358354 2.55352047 .....
这里是您如何计算每个样本的损失:
import numpy as np
def logloss(true_label, predicted, eps=1e-15):
p = np.clip(predicted, eps, 1 - eps)
if true_label == 1:
return -np.log(p)
else:
return -np.log(1 - p)
让我们检查一些虚拟数据(我们实际上不需要模型):
predictions = np.array([0.25,0.65,0.2,0.51,
0.01,0.1,0.34,0.97])
targets = np.array([1,0,0,0,
0,0,0,1])
ll = [logloss(x,y) for (x,y) in zip(targets, predictions)]
ll
# result:
[1.3862943611198906,
1.0498221244986778,
0.2231435513142097,
0.7133498878774648,
0.01005033585350145,
0.10536051565782628,
0.41551544396166595,
0.030459207484708574]
从上面的数组中,您应该能够使自己相信,与真实标签对应的预测距离越远,损失就越大,正如我们直观地期望的那样。
让我们确认上面的计算与scikit-learn返回的总(平均)损失一致:
from sklearn.metrics import log_loss
ll_sk = log_loss(targets, predictions)
ll_sk
# 0.4917494284709932
np.mean(ll)
# 0.4917494284709932
np.mean(ll) == ll_sk
# True
从here改编的代码。