Learn vocabulary and return document id matrix.

        This is equivalent to fit followed by transform.

        Args:
            X : iterable
            an iterable which yields either str, unicode or file objects.

        Returns:
            list : document id matrix.
            list: label id matrix.

def fit_transform(self, X, y=None, **params):
        """Learn vocabulary and return document id matrix.

        This is equivalent to fit followed by transform.

        Args:
            X : iterable
            an iterable which yields either str, unicode or file objects.

        Returns:
            list : document id matrix.
            list: label id matrix.
        """
        return self.fit(X, y).transform(X, y)