diff --git a/applications/test/IndirectList/Test-IndirectList.C b/applications/test/IndirectList/Test-IndirectList.C
index 6ea616c0ba..2f3a2e45d4 100644
--- a/applications/test/IndirectList/Test-IndirectList.C
+++ b/applications/test/IndirectList/Test-IndirectList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -196,19 +196,23 @@ int main(int argc, char *argv[])
 
         SortList<scalar> sorter1(list1);
 
+        Info<< nl << "Sorted: " << flatOutput(sorter1) << nl;
         Info<< nl << "Sort indices: " << flatOutput(sorter1.indices()) << nl;
 
-        Info<< nl << "Reverse indices: " << flatOutput(sorter1.indices()) << nl;
-
+        // Reverses indices
         sorter1.reverse();
 
-        Info<< nl << "Again indices: " << flatOutput(sorter1.indices()) << nl;
+        Info<< nl << "Reverse: " << flatOutput(sorter1.indices()) << nl;
+
+        sorter1.reset();
+
+        Info<< nl << "Reset indices: " << flatOutput(sorter1.indices()) << nl;
 
         sorter1.reverseSort();
 
         Info<< nl << "Reverse indices: " << flatOutput(sorter1.indices()) << nl;
 
-        Info<< nl << "Sorted  : " << flatOutput(sorter1) << nl;
+        Info<< nl << "Reverse sorted: " << flatOutput(sorter1) << nl;
 
         sorter1.sort(std::greater<scalar>());
 
diff --git a/src/OpenFOAM/containers/IndirectLists/SortList/SortList.H b/src/OpenFOAM/containers/IndirectLists/SortList/SortList.H
index e074413300..54622fe51a 100644
--- a/src/OpenFOAM/containers/IndirectLists/SortList/SortList.H
+++ b/src/OpenFOAM/containers/IndirectLists/SortList/SortList.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,8 +37,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef SortList_H
-#define SortList_H
+#ifndef Foam_SortList_H
+#define Foam_SortList_H
 
 #include "IndirectList.H"
 
@@ -72,13 +72,13 @@ public:
 
     // Member Functions
 
-        //- Return the list of sorted indices. Updated every sort
+        //- Return the list of sorted indices (updated every sort).
         //  Same as addressing()
-        inline const labelUList& indices() const;
+        inline const labelUList& indices() const noexcept;
 
-        //- Return the list of indices. Updated every sort
+        //- Return the list of indices (updated every sort).
         //  Same as addressing()
-        inline labelList& indices();
+        inline labelList& indices() noexcept;
 
         //- Reverse the indices
         inline void reverse();
@@ -94,9 +94,13 @@ public:
         //- Functionally identical to sort with std::less\<T\>()
         inline void sort();
 
-        //- Reverse (stable) sort the list
+        //- Reverse (stable) sort the list.
+        //- Functionally identical to sort with std::greater\<T\>()
         inline void reverseSort();
 
+        //- Sort the list, only retaining unique entries
+        inline void uniqueSort();
+
 
     // Member Operators
 
diff --git a/src/OpenFOAM/containers/IndirectLists/SortList/SortListI.H b/src/OpenFOAM/containers/IndirectLists/SortList/SortListI.H
index 98df2a0ff3..1d01531742 100644
--- a/src/OpenFOAM/containers/IndirectLists/SortList/SortListI.H
+++ b/src/OpenFOAM/containers/IndirectLists/SortList/SortListI.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -32,7 +32,7 @@ License
 template<class T>
 inline Foam::SortList<T>::SortList(const UList<T>& values)
 :
-    IndirectList<T>(values, identity(values.size()))
+    IndirectList<T>(values, labelList())
 {
     sort();
 }
@@ -42,7 +42,7 @@ template<class T>
 template<class Compare>
 inline Foam::SortList<T>::SortList(const UList<T>& values, const Compare& comp)
 :
-    IndirectList<T>(values, identity(values.size()))
+    IndirectList<T>(values, labelList())
 {
     sort<Compare>(comp);
 }
@@ -51,14 +51,14 @@ inline Foam::SortList<T>::SortList(const UList<T>& values, const Compare& comp)
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 template<class T>
-inline const Foam::labelUList& Foam::SortList<T>::indices() const
+inline const Foam::labelUList& Foam::SortList<T>::indices() const noexcept
 {
     return this->addressing();
 }
 
 
 template<class T>
-inline Foam::labelList& Foam::SortList<T>::indices()
+inline Foam::labelList& Foam::SortList<T>::indices() noexcept
 {
     return this->addressing();
 }
@@ -74,10 +74,9 @@ inline void Foam::SortList<T>::reverse()
 template<class T>
 inline void Foam::SortList<T>::reset()
 {
-    const label len = this->values().size();
+    auto& addr = this->indices();
 
-    labelList& addr = this->indices();
-    addr.resize(len);
+    addr.resize_nocopy(this->values().size());
     ListOps::identity(addr);
 }
 
@@ -86,14 +85,11 @@ template<class T>
 template<class Compare>
 inline void Foam::SortList<T>::sort(const Compare& comp)
 {
-    UList<T>& vals = this->values();
-    labelList& addr = this->indices();
+    auto& vals = this->values();
+    auto& addr = this->indices();
 
-    if (addr.size() != vals.size())
-    {
-        addr.resize(vals.size());
-        ListOps::identity(addr);
-    }
+    addr.resize_nocopy(vals.size());
+    ListOps::identity(addr);
 
     std::stable_sort
     (
@@ -107,43 +103,26 @@ inline void Foam::SortList<T>::sort(const Compare& comp)
 template<class T>
 inline void Foam::SortList<T>::sort()
 {
-    UList<T>& vals = this->values();
-    labelList& addr = this->indices();
+    Foam::sortedOrder(this->values(), this->indices());
+}
 
-    if (addr.size() != vals.size())
-    {
-        addr.resize(vals.size());
-        ListOps::identity(addr);
-    }
 
-    // Forward sort of indices
-    std::stable_sort
-    (
-        addr.begin(),
-        addr.end(),
-        [&](label a, label b) -> bool { return vals[a] < vals[b]; }
-    );
+template<class T>
+inline void Foam::SortList<T>::uniqueSort()
+{
+    Foam::uniqueOrder(this->values(), this->indices());
 }
 
 
 template<class T>
 inline void Foam::SortList<T>::reverseSort()
 {
-    UList<T>& vals = this->values();
-    labelList& addr = this->indices();
-
-    if (addr.size() != vals.size())
-    {
-        addr.resize(vals.size());
-        ListOps::identity(addr);
-    }
-
-    // Reverse sort of indices
-    std::stable_sort
+    // Reverse sorted order for indices
+    Foam::sortedOrder
     (
-        addr.begin(),
-        addr.end(),
-        [&](label a, label b) -> bool { return vals[b] < vals[a]; }
+        this->values(),
+        this->indices(),
+        typename UList<T>::greater(this->values())
     );
 }
 
diff --git a/src/OpenFOAM/containers/Lists/SortableList/SortableList.C b/src/OpenFOAM/containers/Lists/SortableList/SortableList.C
index 20f9fd02e6..70cc75a575 100644
--- a/src/OpenFOAM/containers/Lists/SortableList/SortableList.C
+++ b/src/OpenFOAM/containers/Lists/SortableList/SortableList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2021 OpenCFD Ltd.
+    Copyright (C) 2017-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -143,7 +143,7 @@ void Foam::SortableList<T>::reverseSort()
 template<class T>
 void Foam::SortableList<T>::partialSort(label n, label start)
 {
-    indices_.resize(this->size());
+    indices_.resize_nocopy(this->size());
     ListOps::identity(indices_);
 
     // Forward partial sort of indices
@@ -163,7 +163,7 @@ void Foam::SortableList<T>::partialSort(label n, label start)
 template<class T>
 void Foam::SortableList<T>::partialReverseSort(label n, label start)
 {
-    indices_.resize(this->size());
+    indices_.resize_nocopy(this->size());
     ListOps::identity(indices_);
 
     // Reverse partial sort of indices