docs: def build_plane_arrays(x, y, qlist):
      """Build a 2-D array out of data taken in the same plane, for contour
      plotting.
      """
      if type(qlist) is not list:
          return_list = False
          qlist = [qlist]
      else:
          return_list = True
      xv = x[np.where(y==y[0])[0]]
      yv = y[np.where(x==x[0])[0]]
      qlistp = []
      for n in range(len(qlist)):
          qlistp.append(np.zeros((len(yv), len(xv))))
      for j in range(len(qlist)):
          for n in range(len(yv)):
              i = np.where(y==yv[n])[0]
              qlistp[j][n,:] = qlist[j][i]
      if not return_list:
          qlistp = qlistp[0]
      return xv, yv, qlistp