code: public ProvenancedConfusionMatrix<CellFiller> filteredCopy(Predicate<CellFiller> predicate) {
      final ImmutableTable.Builder<Symbol, Symbol, List<CellFiller>> newTable =
          ImmutableTable.builder();
  
      for (final Cell<Symbol, Symbol, List<CellFiller>> curCell : table.cellSet()) {
        final List<CellFiller> newFiller = FluentIterable.from(curCell.getValue())
            .filter(predicate).toList();
        if (!newFiller.isEmpty()) {
          newTable.put(curCell.getRowKey(), curCell.getColumnKey(), newFiller);
        }
  
      }
  
      return new ProvenancedConfusionMatrix<CellFiller>(newTable.build());
    }
docs: Return a new {@code ProvenancedConfusionMatrix} containing only those provenance entries
  matching the provided predicate.