@Override
  public RandomAccessDocIdSet getRandomAccessDocIdSet(BoboIndexReader reader) throws IOException {
    final FacetDataCache facetDataCache = dataCacheBuilder.build(reader);
    int startDocIdTemp = Integer.MAX_VALUE;
    int endDocIdTemp = -1;
    for (int i = facetPredicate.valueStartIndex(facetDataCache);
        i < facetPredicate.valueEndIndex(facetDataCache);
        i++) {
      if (facetPredicate.evaluateValue(facetDataCache, i)) {
        if (!facetPredicate.evaluateValue(facetDataCache, i)) {
          continue;
        }
        if (startDocIdTemp > facetDataCache.minIDs[i]) {
          startDocIdTemp = facetDataCache.minIDs[i];
        }
        if (endDocIdTemp < facetDataCache.maxIDs[i]) {
          endDocIdTemp = facetDataCache.maxIDs[i];
        }
      }
    }

    final int startDocId = startDocIdTemp;
    final int endDocId = endDocIdTemp;

    if (startDocId > endDocId) {
      return EmptyDocIdSet.getInstance();
    }
    return new RandomAccessDocIdSet() {
      @Override
      public boolean get(int docId) {
        return facetPredicate.evaluate(facetDataCache, docId);
      }

      @Override
      public DocIdSetIterator iterator() throws IOException {

        return new PredicateDocIdIterator(startDocId, endDocId, facetPredicate, facetDataCache);
      }
    };
  }
 @Override
 public double getFacetSelectivity(BoboIndexReader reader) {
   FacetDataCache dataCache = dataCacheBuilder.build(reader);
   int[] frequencies = dataCache.freqs;
   double selectivity = 0;
   int accumFreq = 0;
   int total = reader.maxDoc();
   for (int i = facetPredicate.valueStartIndex(dataCache);
       i < facetPredicate.valueEndIndex(dataCache);
       i++) {
     if (!facetPredicate.evaluateValue(dataCache, i)) {
       continue;
     }
     accumFreq += frequencies[i];
   }
   selectivity = (double) accumFreq / (double) total;
   if (selectivity > 0.999) {
     selectivity = 1.0;
   }
   return selectivity;
 }