<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def fit(self, dataset):
 """ Computes the mean and variance and stores as a model to be used for later scaling. :param dataset: The data used to compute the mean and variance to build the transformation model. :return: a StandardScalarModel """

        dataset = dataset.map(_convert_to_vector)
        jmodel = callMLlibFunc("fitStandardScaler", self.withMean, self.withStd, dataset)
        return StandardScalerModel(jmodel)