sklearn.metrics
.normalized_mutual_info_score¶

sklearn.metrics.
normalized_mutual_info_score
(labels_true, labels_pred)[source]¶ Normalized Mutual Information between two clusterings
Normalized Mutual Information (NMI) is an normalization of the Mutual Information (MI) score to scale the results between 0 (no mutual information) and 1 (perfect correlation). In this function, mutual information is normalized by
sqrt(H(labels_true) * H(labels_pred))
This measure is not adjusted for chance. Therefore
adjusted_mustual_info_score
might be preferred.This metric is independent of the absolute values of the labels: a permutation of the class or cluster label values won’t change the score value in any way.
This metric is furthermore symmetric: switching
label_true
withlabel_pred
will return the same score value. This can be useful to measure the agreement of two independent label assignments strategies on the same dataset when the real ground truth is not known.Parameters: labels_true : int array, shape = [n_samples]
A clustering of the data into disjoint subsets.
labels_pred : array, shape = [n_samples]
A clustering of the data into disjoint subsets.
Returns: nmi: float :
score between 0.0 and 1.0. 1.0 stands for perfectly complete labeling
See also
adjusted_rand_score
 Adjusted Rand Index
adjusted_mutual_info_score
 Adjusted Mutual Information (adjusted against chance)
Examples
Perfect labelings are both homogeneous and complete, hence have score 1.0:
>>> from sklearn.metrics.cluster import normalized_mutual_info_score >>> normalized_mutual_info_score([0, 0, 1, 1], [0, 0, 1, 1]) 1.0 >>> normalized_mutual_info_score([0, 0, 1, 1], [1, 1, 0, 0]) 1.0
If classes members are completely split across different clusters, the assignment is totally incomplete, hence the NMI is null:
>>> normalized_mutual_info_score([0, 0, 0, 0], [0, 1, 2, 3]) 0.0