def fitting_data(self, data):
        """
        Function to format data for cluster fitting.

        Parameters
        ----------
        data : dict
            A dict of data, containing all elements of
            `analytes` as items.

        Returns
        -------
        A data array for initial cluster fitting.
        """
        ds_fit, _ = self.format_data(data, scale=False)

        # define scaler
        self.scaler = preprocessing.StandardScaler().fit(ds_fit)

        # scale data and return
        return self.scaler.transform(ds_fit)