code: def transform(self, maps):
          
          mass1 = maps[parameters.mass1]
          mass2 = maps[parameters.mass2]
          out = {}
          out[parameters.spin1z] = \
                           conversions.spin1z_from_mass1_mass2_chi_eff_chi_a(
                                 mass1, mass2,
                                 maps[parameters.chi_eff], maps["chi_a"])
          out[parameters.spin2z] = \
                           conversions.spin2z_from_mass1_mass2_chi_eff_chi_a(
                                 mass1, mass2,
                                 maps[parameters.chi_eff], maps["chi_a"])
          return self.format_output(maps, out)
docs: This function transforms from aligned mass-weighted spins to
          cartesian spins aligned along the z-axis.
  
          Parameters
          ----------
          maps : a mapping object
  
          Returns
          -------
          out : dict
              A dict with key as parameter name and value as numpy.array or float
              of transformed values.