Fit base estimators.

        Parameters
        ----------
        X : array-like, shape = (n_samples, n_features)
            Training data.

        y : array-like, optional
            Target data if base estimators are supervised.

        Returns
        -------
        self

def fit(self, X, y=None, **fit_params):
        """Fit base estimators.

        Parameters
        ----------
        X : array-like, shape = (n_samples, n_features)
            Training data.

        y : array-like, optional
            Target data if base estimators are supervised.

        Returns
        -------
        self
        """
        X = numpy.asarray(X)
        self._fit_estimators(X, y, **fit_params)
        Xt = self._predict_estimators(X)
        self.meta_estimator.fit(Xt, y)

        return self