def __init__(self, class_vector, batch_size):
        """
        Arguments
        ---------
        class_vector : torch tensor
            a vector of class labels
        batch_size : integer
            batch_size
        """
        self.class_vector = class_vector
        self.batch_size = batch_size
        self.num_iter = len(class_vector) // 52
        self.n_class = 14
        self.sample_n = 2
        # create pool of each vectors
        indices = {}
        for i in range(self.n_class):
            indices[i] = np.where(self.class_vector == i)[0]

        self.indices = indices
        self.background_index = np.argmax([ len(indices[i]) for i in range(self.n_class)])

        Arguments
        ---------
        class_vector : torch tensor
            a vector of class labels
        batch_size : integer
            batch_size
        
test_classification.py