docs: def _order_linkage_group(group):
      """ For a given group (ie: a list containing [marker, position])
      order the list according to their position.
      """
      tmp = {}
      for row in group:
          if float(row[1]) in tmp:  # pragma: no cover
              tmp[float(row[1])].append(row[0])
          else:
              tmp[float(row[1])] = [row[0]]
  
      keys = list(tmp.keys())
      keys.sort()
      output = []
      for key in keys:
          for entry in tmp[key]:
              if not entry:
                  continue
              output.append([entry, str(key)])
      return output