def fit(self, data=None):
        """
        Performs clustering.rst

        :param data: Data to be fit
        :return: the clustering.rst object
        """
        if self.is_pyclustering_instance(self.model):
            if isinstance(self.model, xmeans):
                data = self.input_preprocess(data)
                self.model._xmeans__pointer_data = data
            elif isinstance(self.model, clarans):
                data = self.input_preprocess(data)
                self.model._clarans__pointer_data = data

            self.model.process()
        else:
            self.model.fit(data)
            return self