I am using MLPClassifer example from scikit-learn

The code for training:

from sklearn.neural_network import MLPClassifier
X = [[0., 0.], [1., 1.]]
y = [0, 1]
clf = MLPClassifier(solver='lbfgs', alpha=1e-5,
                    hidden_layer_sizes=(5, 2), random_state=1)

clf.fit(X, y)                         

At the predict step, we use test data [2., 2.], [-1., -2.] in clf.predict([[2., 2.], [-1., -2.]]). The output of this function is array([1, 0])

As we observe, the test data [2.,2.] is not in the train dataset we passed. Still, we got the closest match as label 1.

What i am trying to find is if the test data i supplied is not in the train dataset, i should print a message to user that data is not valid instead of telling him the wrong label as 1.

For instance, in knn classification, i have kneighbours function which tells the distance of my closest neighbours to the test data i supplied in a 0 to 1 scale. So, i could easily eliminate the test data samples which are highly distant from my train data samples by keeping threshold at 0.6 or 0.7.

Is there any criteria/threshold like this i could do with MLPClassifier or with any one of Incremental Classifiers mentioned here which can restrict my test samples if not present in train dataset ?

Question migrated from SO


1 Answer 1


SGDClassifier has desicion_function which tells the distance to the hyperplane, where the values are compared to.

This value could imply too big and too low values.

  • $\begingroup$ Thanks mico. I see that decision function have values in negative scale, 0 and positive scale. when i do decive_function(untrained_sample), it is showing all negative values in comparision with all the trian data. So, can i be sure that the unknown_sample i passed is always bearing a negatve value and set threshold to consider only those values above 0 for a close match ? $\endgroup$
    – user1
    Mar 7, 2018 at 16:58
  • $\begingroup$ I am not sure. You could test with four values: one above the 1, one below 0 and two between them, one closer to 1 and one closer to 0. And of course for comparison 1 and 0. Then you have the cases tested for sure. Put these as inputs and make observations. $\endgroup$
    – mico
    Mar 7, 2018 at 17:24
  • $\begingroup$ Thanks mico. For fit, all closest samples are above 0. So, i can keep threshold above 0. But for partial_fit(), it is not the case. The scale is varying. The untrained samples also hold positive values (above 0). Have to play around to find the exact number incase of partial_fit(). Any ideas for partial_fit() ? $\endgroup$
    – user1
    Mar 9, 2018 at 10:38

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