docs: def filter_by_maf(min_maf=0.01):
      """
      return function that filters by maf
      (takes minimum maf, default is 0.01)
      """
  
      def f(G, bim):
          maf = 0.5 * G.mean(0)
          maf[maf > 0.5] = 1.0 - maf[maf > 0.5]
          Isnp = maf > min_maf
          G_out = G[:, Isnp]
          bim_out = bim[Isnp]
          return G_out, bim_out
  
      return f