def pseudonymize(self, size=None):
    """
    Return pseudonymized values for this attribute, which is used to
    substitute identifiable data with a reversible, consistent value.
    """
    size = size or self.size
    if size != self.size:
        attr = Series(np.random.choice(self.bins, size=size, p=self.prs))
    else:
        attr = self
    if self.categorical:
        mapping = {b: utils.pseudonymise_string(b) for b in self.bins}
        return attr.map(lambda x: mapping[x])

    if self.type == 'string':
        return attr.map(utils.pseudonymise_string)
    elif self.is_numerical or self.type == 'datetime':
        return attr.map(str).map(utils.pseudonymise_string)