code: def _count_PIS(seqsamp, N):
      
      counts = [Counter(col) for col in seqsamp.T if not ("-" in col or "N" in col)]
      pis = [i.most_common(2)[1][1] > 1 for i in counts if len(i.most_common(2))>1]
      if sum(pis) >= N:
          return sum(pis)
      else:
          return 0
docs: filters for loci with >= N PIS