diff --git a/applications/test/HashTable1/Test-HashTable1.C b/applications/test/HashTable1/Test-HashTable1.C
index 6f92ffcd8f..75e4eeda2d 100644
--- a/applications/test/HashTable1/Test-HashTable1.C
+++ b/applications/test/HashTable1/Test-HashTable1.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.
@@ -33,7 +33,7 @@ License
 #include "IOstreams.H"
 #include "StringStream.H"
 #include "ListOps.H"
-#include "StringListOps.H"
+#include "stringListOps.H"
 
 using namespace Foam;
 
@@ -71,9 +71,18 @@ int main()
         << "table1 [" << table1.size() << "] " << endl;
     forAllConstIters(table1, iter)
     {
-        Info<< iter.key() << " => " << iter() << nl;
+        Info<< iter.key() << " => " << iter.val() << nl;
     }
 
+
+    Info<< "\ntable1 sorted() :" << endl;
+    for (const auto& iter : table1.sorted())
+    {
+        Info<< "    " << iter.key() << " => " << iter.val() << nl;
+    }
+    Info<< endl;
+
+
     table1.set("acr", 108);
     table1.set("adx", 109);
     table1.set("aec", 100);
@@ -82,6 +91,22 @@ int main()
 
     Info<< "\noverwrote some values table1: " << table1 << endl;
 
+
+    // Test writable sorted access
+    for (auto& iter : table1.sorted())
+    {
+        // Should not compile:  iter.key() = "illegal";
+        iter.val() *= 2;
+    }
+
+    Info<< "\nInplace modified - via sorted() access :" << endl;
+    for (const auto& iter : table1.sorted())
+    {
+        Info<< "    " << iter.key() << " => " << iter.val() << nl;
+    }
+    Info<< endl;
+
+
     Info<< "\ntest find:" << endl;
     Info<< table1.find("aaa")() << nl
         << table1.find("aba")() << nl
diff --git a/applications/test/ITstream/Test-ITstream.C b/applications/test/ITstream/Test-ITstream.C
index 1503a43977..30d74df2ab 100644
--- a/applications/test/ITstream/Test-ITstream.C
+++ b/applications/test/ITstream/Test-ITstream.C
@@ -34,7 +34,7 @@ Description
 #include "argList.H"
 #include "ITstream.H"
 #include "ListOps.H"
-#include "StringListOps.H"
+#include "stringListOps.H"
 
 using namespace Foam;
 
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.C b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.C
index c4801b8c80..fac18c0c67 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.C
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.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.
@@ -26,12 +26,13 @@ License
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef HashTable_C
-#define HashTable_C
+#ifndef Foam_HashTable_C
+#define Foam_HashTable_C
 
 #include "HashTable.H"
 #include "List.H"
 #include "FixedList.H"
+#include "UPtrList.H"
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -156,6 +157,45 @@ Foam::List<Key> Foam::HashTable<T, Key, Hash>::sortedToc
 }
 
 
+template<class T, class Key, class Hash>
+Foam::UPtrList<const typename Foam::HashTable<T, Key, Hash>::node_type>
+Foam::HashTable<T, Key, Hash>::sorted() const
+{
+    UPtrList<const node_type> list(size_);
+
+    label count = 0;
+
+    for (const_iterator iter = cbegin(); iter != cend(); ++iter)
+    {
+        list.set(count++, iter.node());
+    }
+
+    Foam::sort(list);
+
+    return list;
+}
+
+
+template<class T, class Key, class Hash>
+Foam::UPtrList<typename Foam::HashTable<T, Key, Hash>::node_type>
+Foam::HashTable<T, Key, Hash>::sorted()
+{
+    UPtrList<node_type> list(size_);
+
+    label count = 0;
+
+    for (iterator iter = begin(); iter != end(); ++iter)
+    {
+        list.set(count++, iter.node());
+    }
+
+    Foam::sort(list);
+
+    return list;
+}
+
+
+
 template<class T, class Key, class Hash>
 template<class UnaryPredicate>
 Foam::List<Key> Foam::HashTable<T, Key, Hash>::tocKeys
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
index 7296b8c18d..cbcdd84179 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
@@ -34,7 +34,8 @@ Description
     depends on the method used to generate the hash key index, the
     table capacity, insertion order etc. When the key order is
     important, use the sortedToc() method to obtain a list of sorted
-    keys and use that for further access.
+    keys and use that for further access, or the sorted() method
+    to obtain a UPtrList of entries to traverse in sorted order.
 
     Internally the table uses closed addressing into a flat storage space
     with collisions handled by linked-list chaining.
@@ -80,8 +81,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef HashTable_H
-#define HashTable_H
+#ifndef Foam_HashTable_H
+#define Foam_HashTable_H
 
 #include "word.H"
 #include "zero.H"
@@ -102,6 +103,7 @@ namespace Foam
 
 template<class T> class List;
 template<class T> class UList;
+template<class T> class UPtrList;
 template<class T, unsigned N> class FixedList;
 template<class T, class Key, class Hash> class HashTable;
 
@@ -120,9 +122,15 @@ class HashTable
 :
     public HashTableCore
 {
-    // Types
+public:
 
-        //- Table entry. A hashed node with a linked-list for collisions
+    // Data Types
+
+        //- The template instance used for this HashTable
+        typedef HashTable<T, Key, Hash> this_type;
+
+        //- A table entry (node) that encapsulates the key/val tuple
+        //- with an additional linked-list entry for hash collisions
         typedef typename std::conditional
         <
             std::is_same<zero::null, typename std::remove_cv<T>::type>::value,
@@ -131,42 +139,6 @@ class HashTable
         >::type node_type;
 
 
-    // Private Data
-
-        //- The number of nodes currently stored in table
-        label size_;
-
-        //- Number of nodes allocated in table
-        label capacity_;
-
-        //- The table of primary nodes
-        node_type** table_;
-
-
-    // Private Member Functions
-
-        //- Return the hash index of the Key within the current table size.
-        //  No checks for zero-sized tables.
-        inline label hashKeyIndex(const Key& key) const;
-
-        //- Assign a new hash-entry to a possibly already existing key.
-        //  \return True if the new entry was set.
-        template<class... Args>
-        bool setEntry(const bool overwrite, const Key& key, Args&&... args);
-
-        //- Read hash table
-        Istream& readTable(Istream& is);
-
-        //- Write hash table
-        Ostream& writeTable(Ostream& os) const;
-
-
-public:
-
-    //- The template instance used for this HashTable
-    typedef HashTable<T, Key, Hash> this_type;
-
-
     // STL type definitions
 
         //- The second template parameter, type of keys used.
@@ -209,6 +181,39 @@ public:
         //- Forward iterator with const access
         class const_iterator;
 
+
+private:
+
+    // Private Data
+
+        //- The number of nodes currently stored in table
+        label size_;
+
+        //- Number of nodes allocated in table
+        label capacity_;
+
+        //- The table of primary nodes
+        node_type** table_;
+
+
+    // Private Member Functions
+
+        //- Return the hash index of the Key within the current table size.
+        //  No checks for zero-sized tables.
+        inline label hashKeyIndex(const Key& key) const;
+
+        //- Assign a new hash-entry to a possibly already existing key.
+        //  \return True if the new entry was set.
+        template<class... Args>
+        bool setEntry(const bool overwrite, const Key& key, Args&&... args);
+
+        //- Read hash table
+        Istream& readTable(Istream& is);
+
+        //- Write hash table
+        Ostream& writeTable(Ostream& os) const;
+
+
 protected:
 
         //- Internally used base for iterator and const_iterator
@@ -220,6 +225,7 @@ protected:
         //- An iterator with non-const access to HashTable internals.
         friend class Iterator<false>;
 
+
 public:
 
     // Constructors
@@ -336,6 +342,17 @@ public:
         ) const;
 
 
+    // Sorted entries
+
+        //- Const access to the hash-table contents in sorted order
+        //- (sorted by keys).
+        UPtrList<const node_type> sorted() const;
+
+        //- Non-const access to the hash-table contents in sorted order
+        //- (sorted by keys).
+        UPtrList<node_type> sorted();
+
+
     // Counting
 
         //- Count the number of keys that satisfy the unary predicate
@@ -701,6 +718,7 @@ public:
             using iterator_category = std::forward_iterator_tag;
             using difference_type   = this_type::difference_type;
 
+            using node_type   = this_type::node_type;
             using key_type    = this_type::key_type;
             using mapped_type = this_type::mapped_type;
             using value_type  = this_type::value_type;
@@ -724,25 +742,37 @@ public:
 
         // Member Functions/Operators
 
+            //- Const access to the entry (node)
+            const node_type* node() const noexcept
+            {
+                return Iterator<false>::entry_;
+            }
+
+            //- Non-const access to the entry (node)
+            node_type* node() noexcept
+            {
+                return Iterator<false>::entry_;
+            }
+
             //- Const access to referenced object (value)
-            inline const_reference val() const
+            const_reference val() const
             {
                 return Iterator<false>::entry_->cval();
             }
 
             //- Non-const access to referenced object (value)
-            inline reference val()
+            reference val()
             {
                 return Iterator<false>::entry_->val();
             }
 
             //- Const access to referenced object (value)
-            inline const_reference operator*() const  { return this->val(); }
-            inline const_reference operator()() const { return this->val(); }
+            const_reference operator*() const  { return this->val(); }
+            const_reference operator()() const { return this->val(); }
 
             //- Non-const access to referenced object (value)
-            inline reference operator*()  { return this->val(); }
-            inline reference operator()() { return this->val(); }
+            reference operator*()  { return this->val(); }
+            reference operator()() { return this->val(); }
 
             inline iterator& operator++();
             inline iterator operator++(int);
@@ -762,6 +792,7 @@ public:
             using iterator_category = std::forward_iterator_tag;
             using difference_type   = this_type::difference_type;
 
+            using node_type   = this_type::node_type;
             using key_type    = this_type::key_type;
             using mapped_type = const this_type::mapped_type;
             using value_type  = const this_type::value_type;
@@ -799,15 +830,21 @@ public:
 
         // Member Functions/Operators
 
+            //- Const access to the entry (node)
+            const node_type* node() const noexcept
+            {
+                return Iterator<true>::entry_;
+            }
+
             //- Const access to referenced object (value)
-            inline reference val() const
+            reference val() const
             {
                 return Iterator<true>::entry_->cval();
             }
 
             //- Const access to referenced object (value)
-            inline reference operator*() const  { return this->val(); }
-            inline reference operator()() const { return this->val(); }
+            reference operator*() const  { return this->val(); }
+            reference operator()() const { return this->val(); }
 
             inline const_iterator& operator++();
             inline const_iterator operator++(int);
@@ -853,8 +890,8 @@ public:
             {}
 
             //- Return the key
-            inline reference operator*() const  { return this->key(); }
-            inline reference operator()() const { return this->key(); }
+            reference operator*() const  { return this->key(); }
+            reference operator()() const { return this->key(); }
 
             inline key_iterator_base& operator++()
             {
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
index 5272915538..dadd621297 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
@@ -34,8 +34,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef HashTableDetail_H
-#define HashTableDetail_H
+#ifndef Foam_HashTableDetail_H
+#define Foam_HashTableDetail_H
 
 #include "zero.H"
 #include <memory>
@@ -73,13 +73,13 @@ template<class T> struct isPointerLike<std::unique_ptr<T>> : std::true_type {};
 \*---------------------------------------------------------------------------*/
 
 //- Internal storage type for HashTable entries
-//  Structure with a (K,V) tuple and a linked-list for collisions
+//  Comprises a (K,V) tuple and a linked-list entry for hash collisions.
 //  Could store key/val as std::pair, but no particular advantage
 //  unless the iterator dereference type changes.
 template<class K, class V>
 struct HashTablePair
 {
-    // Types
+    // Data Types
 
         //- Type of key
         typedef K key_type;
@@ -87,26 +87,26 @@ struct HashTablePair
         //- Type of content
         typedef V mapped_type;
 
-        //- This struct stores a value
+        //- This class stores a value
         static constexpr bool stores_value() noexcept
         {
             return true;
         }
 
 
-    // Member Data
+    // Data
 
         //- The lookup key
-        key_type key_;
+        const K key_;
 
         //- The mapped data
-        mapped_type val_;
+        V val_;
 
         //- Addressing (next in collision list)
         HashTablePair* next_;
 
 
-    // Member Functions
+    // Generated Methods
 
         //- No copy construct
         HashTablePair(const HashTablePair&) = delete;
@@ -115,6 +115,8 @@ struct HashTablePair
         void operator=(const HashTablePair&) = delete;
 
 
+    // Constructors
+
         //- Construct from next pointer, key, contents
         template<class... Args>
         HashTablePair
@@ -130,24 +132,39 @@ struct HashTablePair
         {}
 
 
+    // Member Functions
+
         //- The key
-        const key_type& key() const
+        const key_type& key() const noexcept
         {
             return key_;
         }
 
         //- Const access to the mapped value
-        const mapped_type& cval() const
+        const mapped_type& cval() const noexcept
+        {
+            return val_;
+        }
+
+        //- Const access to the mapped value
+        const mapped_type& val() const noexcept
         {
             return val_;
         }
 
         //- Non-const access to the mapped value
-        mapped_type& val()
+        mapped_type& val() noexcept
         {
             return val_;
         }
 
+
+        //- Compare keys
+        bool operator<(const HashTablePair& rhs) const
+        {
+            return key_ < rhs.key_;
+        }
+
         //- Write (key, val) pair - for pointer types
         template<class TypeT = V>
         typename std::enable_if
@@ -190,38 +207,38 @@ struct HashTablePair
 \*---------------------------------------------------------------------------*/
 
 //- Internal storage type for HashSet entries
-//  Structure with a single (K) value and a linked-list for collisions
+//  Comprises a single (K) value and a linked-list entry for hash collisions
 template<class K>
 struct HashTableSingle
 {
-    // Types
+    // Data Types
 
         //- Type of key
         typedef K key_type;
 
-        //- Type of content
+        //- Type of content (no content: placeholder)
         typedef Foam::zero::null mapped_type;
 
         //- Content storage type to the entry
         typedef key_type value_type;
 
-        //- This struct does not store a value
+        //- This class does not store any value
         static constexpr bool stores_value() noexcept
         {
             return false;
         }
 
 
-    // Member Data
+    // Data
 
         //- The lookup key == content
-        key_type key_;
+        const K key_;
 
         //- Addressing (next in collision list)
         HashTableSingle* next_;
 
 
-    // Member Functions
+    // Generated Methods
 
         //- No copy construct
         HashTableSingle(const HashTableSingle&) = delete;
@@ -230,6 +247,8 @@ struct HashTableSingle
         void operator=(const HashTableSingle&) = delete;
 
 
+    // Constructors
+
         //- Construct from next pointer, key, (unused) contents
         template<class... Args>
         HashTableSingle
@@ -244,25 +263,40 @@ struct HashTableSingle
         {}
 
 
+    // Member Functions
+
         //- The key
-        const key_type& key() const
+        const key_type& key() const noexcept
         {
             return key_;
         }
 
         //- Const access to the (dummy) mapped value
-        const mapped_type& cval() const
+        const mapped_type& cval() const noexcept
+        {
+            return Foam::zero::null::dummy;
+        }
+
+        //- Const access to the (dummy) mapped value
+        const mapped_type& val() const noexcept
         {
             return Foam::zero::null::dummy;
         }
 
         //- Non-const access to the (dummy) mapped value
-        mapped_type& val()
+        mapped_type& val() noexcept
         {
             return Foam::zero::null::dummy;
         }
 
-        //- Write the key. There is no value
+
+        //- Compare keys
+        bool operator<(const HashTableSingle& rhs) const
+        {
+            return key_ < rhs.key_;
+        }
+
+        //- Write the key. There is no value to write.
         void print(Ostream& os) const
         {
             os << key_;