Fit label encoder and return encoded labels

        Parameters
        ----------
        y : array-like of shape [n_samples]
            Target values.

        Returns
        -------
        y : array-like of shape [n_samples]

def fit_transform(self, X, y=None, **fit_params):
        """Fit label encoder and return encoded labels

        Parameters
        ----------
        y : array-like of shape [n_samples]
            Target values.

        Returns
        -------
        y : array-like of shape [n_samples]
        """
        y = column_or_1d(X, warn=True)
        _check_numpy_unicode_bug(X)
        self.classes_, X = np.unique(X, return_inverse=True)
        return X