docs: def printUniqueTFAM(tfam, samples, prefix):
      """Prints a new TFAM with only unique samples.
  
      :param tfam: a representation of a TFAM file.
      :param samples: the position of the samples
      :param prefix: the prefix of the output file name
  
      :type tfam: list
      :type samples: dict
      :type prefix: str
  
      """
      fileName = prefix + ".unique_samples.tfam"
      try:
          with open(fileName, "w") as outputFile:
              for i in sorted(samples.values()):
                  print >>outputFile, "\t".join(tfam[i])
      except IOError:
          msg = "%(fileName)s: no such file"
          raise ProgramError(msg)