sklearn.metrics
.log_loss¶

sklearn.metrics.
log_loss
(y_true, y_pred, eps=1e15, normalize=True, sample_weight=None, labels=None)[source]¶ Log loss, aka logistic loss or crossentropy loss.
This is the loss function used in (multinomial) logistic regression and extensions of it such as neural networks, defined as the negative loglikelihood of the true labels given a probabilistic classifier’s predictions. The log loss is only defined for two or more labels. For a single sample with true label yt in {0,1} and estimated probability yp that yt = 1, the log loss is
log P(ytyp) = (yt log(yp) + (1  yt) log(1  yp))
Read more in the User Guide.
 Parameters
 y_truearraylike or label indicator matrix
Ground truth (correct) labels for n_samples samples.
 y_predarraylike of float, shape = (n_samples, n_classes) or (n_samples,)
Predicted probabilities, as returned by a classifier’s predict_proba method. If
y_pred.shape = (n_samples,)
the probabilities provided are assumed to be that of the positive class. The labels iny_pred
are assumed to be ordered alphabetically, as done bypreprocessing.LabelBinarizer
. epsfloat
Log loss is undefined for p=0 or p=1, so probabilities are clipped to max(eps, min(1  eps, p)).
 normalizebool, optional (default=True)
If true, return the mean loss per sample. Otherwise, return the sum of the persample losses.
 sample_weightarraylike of shape (n_samples,), default=None
Sample weights.
 labelsarraylike, optional (default=None)
If not provided, labels will be inferred from y_true. If
labels
isNone
andy_pred
has shape (n_samples,) the labels are assumed to be binary and are inferred fromy_true
. .. versionadded:: 0.18
 Returns
 lossfloat
Notes
The logarithm used is the natural logarithm (basee).
References
C.M. Bishop (2006). Pattern Recognition and Machine Learning. Springer, p. 209.
Examples
>>> from sklearn.metrics import log_loss >>> log_loss(["spam", "ham", "ham", "spam"], ... [[.1, .9], [.9, .1], [.8, .2], [.35, .65]]) 0.21616...