Getting the accuracy for multi-label prediction in scikit-learn

Question

In a multilabel classification setting, sklearn.metrics.accuracy_score only computes the subset accuracy (3): i.e. the set of labels predicted for a sample must exactly match the corresponding set of labels in y_true.

This way of computing the accuracy is sometime named, perhaps less ambiguously, exact match ratio (1):

Is there any way to get the other typical way to compute the accuracy in scikit-learn, namely

(as defined in (1) and (2), and less ambiguously referred to as the Hamming score (4) (since it is closely related to the Hamming loss), or label-based accuracy) ?

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(1) Sorower, Mohammad S. "A literature survey on algorithms for multi-label learning." Oregon State University, Corvallis (2010).

(2) Tsoumakas, Grigorios, and Ioannis Katakis. "Multi-label classification: An overview." Dept. of Informatics, Aristotle University of Thessaloniki, Greece (2006).

(3) Ghamrawi, Nadia, and Andrew McCallum. "Collective multi-label classification." Proceedings of the 14th ACM international conference on Information and knowledge management. ACM, 2005.

(4) Godbole, Shantanu, and Sunita Sarawagi. "Discriminative methods for multi-labeled classification." Advances in Knowledge Discovery and Data Mining. Springer Berlin Heidelberg, 2004. 22-30.

Answer 1

You can write one version yourself, here is a example without considering the weight and normalize.

import numpy as np  y_true = np.array([[0,1,0],                    [0,1,1],                    [1,0,1],                    [0,0,1]])  y_pred = np.array([[0,1,1],                    [0,1,1],                    [0,1,0],                    [0,0,0]])  def hamming_score(y_true, y_pred, normalize=True, sample_weight=None):     '''     Compute the Hamming score (a.k.a. label-based accuracy) for the multi-label case     http://stackoverflow.com/q/32239577/395857     '''     acc_list = []     for i in range(y_true.shape[0]):         set_true = set( np.where(y_true[i])[0] )         set_pred = set( np.where(y_pred[i])[0] )         #print('\nset_true: {0}'.format(set_true))         #print('set_pred: {0}'.format(set_pred))         tmp_a = None         if len(set_true) == 0 and len(set_pred) == 0:             tmp_a = 1         else:             tmp_a = len(set_true.intersection(set_pred))/\                     float( len(set_true.union(set_pred)) )         #print('tmp_a: {0}'.format(tmp_a))         acc_list.append(tmp_a)     return np.mean(acc_list)  if __name__ == "__main__":     print('Hamming score: {0}'.format(hamming_score(y_true, y_pred))) # 0.375 (= (0.5+1+0+0)/4)      # For comparison sake:     import sklearn.metrics      # Subset accuracy     # 0.25 (= 0+1+0+0 / 4) --> 1 if the prediction for one sample fully matches the gold. 0 otherwise.     print('Subset accuracy: {0}'.format(sklearn.metrics.accuracy_score(y_true, y_pred, normalize=True, sample_weight=None)))      # Hamming loss (smaller is better)     # $$ \text{HammingLoss}(x_i, y_i) = \frac{1}{|D|} \sum_{i=1}^{|D|} \frac{xor(x_i, y_i)}{|L|}, $$     # where     #  - \\(|D|\\) is the number of samples       #  - \\(|L|\\) is the number of labels       #  - \\(y_i\\) is the ground truth       #  - \\(x_i\\)  is the prediction.       # 0.416666666667 (= (1+0+3+1) / (3*4) )     print('Hamming loss: {0}'.format(sklearn.metrics.hamming_loss(y_true, y_pred)))  

Outputs:

Hamming score: 0.375 Subset accuracy: 0.25 Hamming loss: 0.416666666667 

Answer 2

A simple summary function:

import numpy as np  def hamming_score(y_true, y_pred):     return (         (y_true & y_pred).sum(axis=1) / (y_true | y_pred).sum(axis=1)     ).mean()   hamming_score(y_true, y_pred) # 0.375