diff --git a/RecoTauTag/RecoTau/plugins/DeepTauId.cc b/RecoTauTag/RecoTau/plugins/DeepTauId.cc
index c38347b3c0125..a5e33f2fa4b8a 100644
--- a/RecoTauTag/RecoTau/plugins/DeepTauId.cc
+++ b/RecoTauTag/RecoTau/plugins/DeepTauId.cc
@@ -299,9 +299,12 @@ struct CellIndex {
 
 class CellGrid {
 public:
-    CellGrid(unsigned _nCellsEta, unsigned _nCellsPhi, double _cellSizeEta, double _cellSizePhi) :
-        nCellsEta(_nCellsEta), nCellsPhi(_nCellsPhi), nTotal(nCellsEta * nCellsPhi),
-        cellSizeEta(_cellSizeEta), cellSizePhi(_cellSizePhi), cells(nTotal)
+    using Map = std::map<CellIndex, Cell>;
+    using const_iterator = Map::const_iterator;
+
+    CellGrid(unsigned n_cells_eta, unsigned n_cells_phi, double cell_size_eta, double cell_size_phi) :
+        nCellsEta(n_cells_eta), nCellsPhi(n_cells_phi), nTotal(nCellsEta * nCellsPhi),
+        cellSizeEta(cell_size_eta), cellSizePhi(cell_size_phi)
     {
         if(nCellsEta % 2 != 1 || nCellsEta < 1)
             throw cms::Exception("DeepTauId") << "Invalid number of eta cells.";
@@ -311,10 +314,12 @@ class CellGrid {
             throw cms::Exception("DeepTauId") << "Invalid cell size.";
     }
 
-    int MaxEtaIndex() const { return static_cast<int>((nCellsEta - 1) / 2); }
-    int MaxPhiIndex() const { return static_cast<int>((nCellsPhi - 1) / 2); }
-    double MaxDeltaEta() const { return cellSizeEta * (0.5 + MaxEtaIndex()); }
-    double MaxDeltaPhi() const { return cellSizePhi * (0.5 + MaxPhiIndex()); }
+    int maxEtaIndex() const { return static_cast<int>((nCellsEta - 1) / 2); }
+    int maxPhiIndex() const { return static_cast<int>((nCellsPhi - 1) / 2); }
+    double maxDeltaEta() const { return cellSizeEta * (0.5 + maxEtaIndex()); }
+    double maxDeltaPhi() const { return cellSizePhi * (0.5 + maxPhiIndex()); }
+    int getEtaTensorIndex(const CellIndex& cellIndex) const { return cellIndex.eta + maxEtaIndex(); }
+    int getPhiTensorIndex(const CellIndex& cellIndex) const { return cellIndex.phi + maxPhiIndex(); }
 
     bool TryGetCellIndex(double deltaEta, double deltaPhi, CellIndex& cellIndex) const
     {
@@ -326,28 +331,21 @@ class CellGrid {
             return true;
         };
 
-        return getCellIndex(deltaEta, MaxDeltaEta(), cellSizeEta, cellIndex.eta)
-               && getCellIndex(deltaPhi, MaxDeltaPhi(), cellSizePhi, cellIndex.phi);
+        return getCellIndex(deltaEta, maxDeltaEta(), cellSizeEta, cellIndex.eta)
+               && getCellIndex(deltaPhi, maxDeltaPhi(), cellSizePhi, cellIndex.phi);
     }
 
-    Cell& at(const CellIndex& cellIndex) { return cells.at(GetFlatIndex(cellIndex)); }
-    const Cell& at(const CellIndex& cellIndex) const { return cells.at(GetFlatIndex(cellIndex)); }
-    bool IsEmpty(const CellIndex& cellIndex) const { return at(cellIndex).empty(); }
-
-private:
-    size_t GetFlatIndex(const CellIndex& cellIndex) const
-    {
-        if(std::abs(cellIndex.eta) > MaxEtaIndex() || std::abs(cellIndex.phi) > MaxPhiIndex())
-            throw cms::Exception("DeepTauId") << "Cell index is out of range";
-        const unsigned shiftedEta = static_cast<unsigned>(cellIndex.eta + MaxEtaIndex());
-        const unsigned shiftedPhi = static_cast<unsigned>(cellIndex.phi + MaxPhiIndex());
-        return shiftedEta * nCellsPhi + shiftedPhi;
-    }
+    Cell& operator[](const CellIndex& cellIndex) { return cells[cellIndex]; }
+    const Cell& at(const CellIndex& cellIndex) const { return cells.at(cellIndex); }
+    const_iterator begin() const { return cells.begin(); }
+    const_iterator end() const { return cells.end(); }
 
-private:
+public:
     const unsigned nCellsEta, nCellsPhi, nTotal;
     const double cellSizeEta, cellSizePhi;
-    std::vector<Cell> cells;
+
+private:
+    std::map<CellIndex, Cell> cells;
 };
 
 } // anonymous namespace
@@ -535,7 +533,7 @@ class DeepTauId : public deep_tau::DeepTauBase {
             const CellObjectType obj_type = GetCellObjectType(obj);
             CellIndex cell_index;
             if(grid.TryGetCellIndex(deta, dphi, cell_index)) {
-                Cell& cell = grid.at(cell_index);
+                Cell& cell = grid[cell_index];
                 auto iter = cell.find(obj_type);
                 if(iter != cell.end()) {
                      const auto& prev_obj = objects.at(iter->second);
@@ -550,7 +548,7 @@ class DeepTauId : public deep_tau::DeepTauBase {
         for(size_t n = 0; n < objects.size(); ++n) {
             const auto& obj = objects.at(n);
             const double deta = obj.polarP4().eta() - tau.polarP4().eta();
-            const double dphi = ROOT::Math::VectorUtil::DeltaPhi(obj.polarP4(), tau.polarP4());
+            const double dphi = ROOT::Math::VectorUtil::DeltaPhi(tau.polarP4(), obj.polarP4());
             const double dR2 = std::pow(deta, 2) + std::pow(dphi, 2);
             if(dR2 < inner_dR2)
                 addObject(n, deta, dphi, inner_grid);