def _preprocess_values(self, Y):
Y_prep = Y.copy()<EOL>Y1 = Y[Y.flatten()==<NUM_LIT:1>].size<EOL>Y2 = Y[Y.flatten()==<NUM_LIT:0>].size<EOL>assert Y1 + Y2 == Y.size, '<STR_LIT>'<EOL>Y_prep[Y.flatten() == <NUM_LIT:0>] = -<NUM_LIT:1><EOL>return Y_prep<EOL>
Check if the values of the observations correspond to the values
assumed by the likelihood function.

..Note:: Binary classification algorithm works better with classes {-1, 1}