docs: def findUniques(mapF):
      """Finds the unique markers in a MAP.
  
      :param mapF: representation of a ``map`` file.
  
      :type mapF: list
  
      :returns: a :py:class:`dict` containing unique markers (according to their
                genomic localisation).
  
      """
      uSNPs = {}
      dSNPs = defaultdict(list)
      for i, row in enumerate(mapF):
          chromosome = row[0]
          position = row[3]
          snpID = (chromosome, position)
          if snpID not in uSNPs:
              # This is the first time we see this sample
              uSNPs[snpID] = i
          else:
              # We have seen this sample at least once...
              if snpID not in dSNPs:
                  # This is the second time we see this sample...
                  dSNPs[snpID].extend([uSNPs[snpID], i])
              else:
                  # We have seen this sample multiple times
                  dSNPs[snpID].append(i)
  
      # Removing the duplicates from the unique samples
      for snpID in dSNPs.iterkeys():
          if snpID in uSNPs:
              del uSNPs[snpID]
  
      return uSNPs