diff --git a/applications/test/HashSet/Test-hashSet.C b/applications/test/HashSet/Test-hashSet.C
index 425320bc39..eeae7ff0d0 100644
--- a/applications/test/HashSet/Test-hashSet.C
+++ b/applications/test/HashSet/Test-hashSet.C
@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2018 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -27,13 +27,50 @@ Description
 
 #include "hashedWordList.H"
 #include "nil.H"
+#include "HashOps.H"
 #include "HashSet.H"
 #include "Map.H"
 #include "labelPairHashes.H"
 #include "FlatOutput.H"
 
+#include <algorithm>
+
 using namespace Foam;
 
+template<class Iter>
+void printIf(const Iter& iter)
+{
+    if (iter.found())
+    {
+        Info<< *iter;
+    }
+    else
+    {
+        Info<<"(null)";
+    }
+}
+
+
+template<class Key, class Hash>
+void printMinMax(const HashSet<Key, Hash>& set)
+{
+    const auto first = set.cbegin();
+    const auto last  = set.cend();
+
+    const auto min = std::min_element(first, last);
+    const auto max = std::max_element(first, last);
+
+    Info<< "set: " << flatOutput(set) << nl;
+    Info<< "    min=";
+    printIf(min);
+    Info<< nl;
+
+    Info<< "    max=";
+    printIf(max);
+    Info<< nl;
+}
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 // Main program:
 
@@ -131,9 +168,14 @@ int main(int argc, char *argv[])
     Info<< "create from Map<label>: ";
     Info<< labelHashSet(mapA) << endl;
 
-    Info<<"combined toc: "
-        << (wordHashSet(setA) | wordHashSet(tableA) | wordHashSet(tableB))
-        << nl;
+    {
+        auto allToc =
+            (wordHashSet(setA) | wordHashSet(tableA) | wordHashSet(tableB));
+
+        Info<<"combined toc: " << flatOutput(allToc) << nl;
+
+        printMinMax(allToc);
+    }
 
     labelHashSet setB
     {
@@ -226,6 +268,12 @@ int main(int argc, char *argv[])
         Info << i << endl;
     }
 
+    printMinMax(setD);
+    Info<< nl;
+
+    printMinMax(labelHashSet());
+    Info<< nl;
+
     Info<< nl << "Test swapping, moving etc." << nl;
     setA.insert({ "some", "more", "entries" });
 
diff --git a/applications/test/List/Test-List.C b/applications/test/List/Test-List.C
index 9ed62a26f9..792705904a 100644
--- a/applications/test/List/Test-List.C
+++ b/applications/test/List/Test-List.C
@@ -43,6 +43,7 @@ See also
 
 #include "labelRange.H"
 #include "scalarList.H"
+#include "HashOps.H"
 #include "ListOps.H"
 #include "SubList.H"
 
@@ -473,7 +474,7 @@ int main(int argc, char *argv[])
         }
 
         {
-            PackedBoolList select(locations.toc());
+            PackedBoolList select = HashSetOps::bitset(locations);
             auto output = ListOps::createWithValue<label>
             (
                 30,
@@ -486,16 +487,7 @@ int main(int argc, char *argv[])
         }
 
         {
-            // Fairly really inconvenient way to set true/false
-            labelList toc(locations.sortedToc());
-
-            List<bool> select = ListOps::createWithValue<bool>
-            (
-                toc.last() + 1,
-                toc,
-                true,
-                false  // default value
-            );
+            List<bool> select = HashSetOps::bools(locations);
 
             auto output = ListOps::createWithValue<label>
             (
@@ -524,7 +516,7 @@ int main(int argc, char *argv[])
         }
 
         {
-            PackedBoolList select(locations.toc());
+            PackedBoolList select = HashSetOps::bitset(locations);
             auto output = ListOps::createWithValue<label>
             (
                 30,
@@ -533,20 +525,12 @@ int main(int argc, char *argv[])
                 -1  // default value
             );
             Info<< "with PackedBoolList: " << flatOutput(output)
-                << " selector: " << flatOutput(select.used()) << nl;
+                << " selector: " << flatOutput(HashSetOps::used(select))
+                << nl;
         }
 
         {
-            // Fairly really inconvenient way to set true/false
-            labelList toc(locations.sortedToc());
-
-            List<bool> select = ListOps::createWithValue<bool>
-            (
-                toc.last() + 1,
-                toc,
-                true,
-                false  // default value
-            );
+            List<bool> select = HashSetOps::bools(locations);
 
             auto output = ListOps::createWithValue<label>
             (
@@ -556,7 +540,8 @@ int main(int argc, char *argv[])
                 -1  // default value
             );
             Info<< "with boolList: " << flatOutput(output)
-                << " selector: " << flatOutput(select) << nl;
+                << " selector: " << flatOutput(HashSetOps::used(select))
+                << nl;
         }
     }
 
diff --git a/applications/utilities/postProcessing/dataConversion/foamToEnsight/findCloudFields.H b/applications/utilities/postProcessing/dataConversion/foamToEnsight/findCloudFields.H
index c7fec95c0a..895da258ab 100644
--- a/applications/utilities/postProcessing/dataConversion/foamToEnsight/findCloudFields.H
+++ b/applications/utilities/postProcessing/dataConversion/foamToEnsight/findCloudFields.H
@@ -62,7 +62,7 @@ if (timeDirs.size() && !noLagrangian)
 
     if (Pstream::parRun())
     {
-        Pstream::mapCombineGather(cloudFields, HashTablePlusEqOp<word>());
+        Pstream::mapCombineGather(cloudFields, HashTableOps::plusEqOp<word>());
         Pstream::mapCombineScatter(cloudFields);
     }
 
diff --git a/applications/utilities/postProcessing/dataConversion/foamToEnsight/foamToEnsight.C b/applications/utilities/postProcessing/dataConversion/foamToEnsight/foamToEnsight.C
index 6633b330b6..4bd3c8aeaf 100644
--- a/applications/utilities/postProcessing/dataConversion/foamToEnsight/foamToEnsight.C
+++ b/applications/utilities/postProcessing/dataConversion/foamToEnsight/foamToEnsight.C
@@ -73,7 +73,7 @@ Note
 #include "IOmanip.H"
 #include "OFstream.H"
 #include "PstreamCombineReduceOps.H"
-#include "HashTableOps.H"
+#include "HashOps.H"
 
 #include "fvc.H"
 #include "volFields.H"
diff --git a/applications/utilities/postProcessing/dataConversion/foamToVTK/findClouds.H b/applications/utilities/postProcessing/dataConversion/foamToVTK/findClouds.H
index 0bc5970d75..2b293f1711 100644
--- a/applications/utilities/postProcessing/dataConversion/foamToVTK/findClouds.H
+++ b/applications/utilities/postProcessing/dataConversion/foamToVTK/findClouds.H
@@ -53,7 +53,7 @@ if (timeDirs.size() && !noLagrangian)
 
     if (Pstream::parRun())
     {
-        Pstream::combineGather(allCloudDirs, HashSetPlusEqOp<word>());
+        Pstream::combineGather(allCloudDirs, HashSetOps::plusEqOp<word>());
         Pstream::combineScatter(allCloudDirs);
     }
 }
diff --git a/applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK.C b/applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK.C
index eb7e697214..7a5351f5cb 100644
--- a/applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK.C
+++ b/applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK.C
@@ -147,7 +147,7 @@ Note
 #include "volPointInterpolation.H"
 #include "emptyPolyPatch.H"
 #include "PstreamCombineReduceOps.H"
-#include "HashTableOps.H"
+#include "HashOps.H"
 #include "labelIOField.H"
 #include "scalarIOField.H"
 #include "sphericalTensorIOField.H"
@@ -1482,7 +1482,7 @@ int main(int argc, char *argv[])
                     Pstream::mapCombineGather
                     (
                         cloudFields,
-                        HashSetPlusEqOp<word>()
+                        HashSetOps::plusEqOp<word>()
                     );
                     Pstream::mapCombineScatter(cloudFields);
                 }
diff --git a/src/OpenFOAM/Make/files b/src/OpenFOAM/Make/files
index ae8af888bf..0ec1cb054f 100644
--- a/src/OpenFOAM/Make/files
+++ b/src/OpenFOAM/Make/files
@@ -145,6 +145,7 @@ primitives/polynomialEqns/quadraticEqn/quadraticEqn.C
 primitives/Barycentric/barycentric/barycentric.C
 primitives/Barycentric2D/barycentric2D/barycentric2D.C
 
+containers/HashTables/HashOps/HashOps.C
 containers/HashTables/HashTable/HashTableCore.C
 containers/Lists/SortableList/ParSortableListName.C
 containers/Lists/PackedList/PackedListCore.C
diff --git a/src/OpenFOAM/containers/HashTables/HashOps/HashOps.C b/src/OpenFOAM/containers/HashTables/HashOps/HashOps.C
new file mode 100644
index 0000000000..494ad5ed4b
--- /dev/null
+++ b/src/OpenFOAM/containers/HashTables/HashOps/HashOps.C
@@ -0,0 +1,122 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "HashOps.H"
+#include "PackedBoolList.H"
+
+#include <algorithm>
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+Foam::labelHashSet Foam::HashSetOps::used(const PackedBoolList& select)
+{
+    const label count = select.count();
+    const label len = select.size();
+
+    labelHashSet output(2*count);
+
+    label used = 0;
+    for (label i = 0; i < len && used < count; ++i)
+    {
+        if (select[i])
+        {
+            output.insert(i);
+            ++used;
+        }
+    }
+
+    return output;
+}
+
+
+Foam::labelHashSet Foam::HashSetOps::used(const UList<bool>& select)
+{
+    // We have no estimate of the size/sparsity, just assume 1/10
+
+    const label len = select.size();
+
+    labelHashSet output(len/10);
+
+    for (label i = 0; i < len; ++i)
+    {
+        if (select[i])
+        {
+            output.insert(i);
+        }
+    }
+
+    return output;
+}
+
+
+Foam::PackedBoolList Foam::HashSetOps::bitset(const labelHashSet& labels)
+{
+    auto const max = std::max_element(labels.cbegin(), labels.cend());
+    const label len = (max.found() ? (1 + *max) : 0);
+
+    if (len <= 0)
+    {
+        return PackedBoolList();
+    }
+
+    PackedBoolList output(len);
+
+    for (const label i : labels)
+    {
+        if (i >= 0)
+        {
+            output.set(i);
+        }
+    }
+
+    return output;
+}
+
+
+Foam::List<bool> Foam::HashSetOps::bools(const labelHashSet& labels)
+{
+    auto const max = std::max_element(labels.cbegin(), labels.cend());
+    const label len = (max.found() ? (1 + *max) : 0);
+
+    if (len <= 0)
+    {
+        return List<bool>();
+    }
+
+    List<bool> output(len, false);
+
+    for (const label i : labels)
+    {
+        if (i >= 0)
+        {
+            output[i] = true;
+        }
+    }
+
+    return output;
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/containers/HashTables/HashOps/HashOps.H b/src/OpenFOAM/containers/HashTables/HashOps/HashOps.H
new file mode 100644
index 0000000000..b19f1aca99
--- /dev/null
+++ b/src/OpenFOAM/containers/HashTables/HashOps/HashOps.H
@@ -0,0 +1,151 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Namspace
+    Foam::HashSetOps
+
+Description
+    Various operations for HashSet.
+
+Namspace
+    Foam::HashTableOps
+
+Description
+    Various operations for HashTable.
+
+SourceFiles
+    HashOps.H
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef HashOps_H
+#define HashOps_H
+
+#include "HashSet.H"
+#include "List.H"
+
+namespace Foam
+{
+
+// Forward declarations
+
+class PackedBoolList;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+/*---------------------------------------------------------------------------*\
+                       Namespace HashSetOps Declaration
+\*---------------------------------------------------------------------------*/
+
+namespace HashSetOps
+{
+
+//- Combine HashSet operation. Equivalent to 'a += b'
+template<class Key=word, class Hash=string::hash>
+struct plusEqOp
+{
+    typedef HashSet<Key, Hash> value_type;
+
+    void operator()(value_type& a, const value_type& b) const
+    {
+        a += b;
+    }
+};
+
+
+//- Convert a packed list of bits to a labelHashSet of the indices used.
+//
+//  \param selection the list for which a 'true' entry corresponds
+//       to an index for be added to the labelHashSet
+//
+//  \return a labelHashSet of the selected indices
+labelHashSet used(const PackedBoolList& select);
+
+
+//- Convert a list of bools to a labelHashSet of the indices used.
+//
+//  \param selection the list for which a 'true' entry corresponds
+//       to an index for be added to the labelHashSet
+//
+//  \return a labelHashSet of the selected indices
+labelHashSet used(const UList<bool>& select);
+
+
+//- Convert labels to a packed list of bits, with '1' for each
+//- non-negative value and '0' for all others.
+//
+//  \param labels the list of indices.
+//
+//  \return a packed bit list of the selected indices
+//
+//  \note The operation discards any negative values since these are
+//     invalid positions in the output list.
+PackedBoolList bitset(const labelHashSet& labels);
+
+
+//- Convert labels to a list of bools, with 'true' for each
+//- non-negative value and 'false' for all others.
+//
+//  \param labels the list of indices.
+//
+//  \return a bool List of the selected indices
+//
+//  \note The operation discards any negative values since these are
+//     invalid positions in the output list.
+List<bool> bools(const labelHashSet& labels);
+
+
+} // End namespace HashSetOps
+
+
+/*---------------------------------------------------------------------------*\
+                      Namespace HashTableOps Declaration
+\*---------------------------------------------------------------------------*/
+
+namespace HashTableOps
+{
+
+//- Combine HashTable operation. Equivalent to 'a += b'
+template<class T, class Key=word, class Hash=string::hash>
+struct plusEqOp
+{
+    typedef HashTable<T, Key, Hash> value_type;
+
+    void operator()(value_type& a, const value_type& b) const
+    {
+        a += b;
+    }
+};
+
+} // End namespace HashTableOps
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/containers/HashTables/HashTableOps/HashTableOps.H b/src/OpenFOAM/containers/HashTables/HashTableOps/HashTableOps.H
deleted file mode 100644
index 20631f776d..0000000000
--- a/src/OpenFOAM/containers/HashTables/HashTableOps/HashTableOps.H
+++ /dev/null
@@ -1,79 +0,0 @@
-/*---------------------------------------------------------------------------*\
-  =========                 |
-  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
-   \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
-     \\/     M anipulation  |
--------------------------------------------------------------------------------
-License
-    This file is part of OpenFOAM.
-
-    OpenFOAM is free software: you can redistribute it and/or modify it
-    under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
-    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
-    for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
-
-InNamspace
-    Foam
-
-Description
-    Various functions to operate on HashTables.
-
-SourceFiles
-    HashTableOps.H
-
-\*---------------------------------------------------------------------------*/
-
-#ifndef HashTableOps_H
-#define HashTableOps_H
-
-#include "HashSet.H"
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-namespace Foam
-{
-
-//- Combine HashSet operation. Equivalent to 'a += b'
-template<class Key=word, class Hash=string::hash>
-struct HashSetPlusEqOp
-{
-    typedef HashSet<Key, Hash> value_type;
-
-    void operator()(value_type& a, const value_type& b) const
-    {
-        a += b;
-    }
-};
-
-
-//- Combine HashTable operation. Equivalent to 'a += b'
-template<class T, class Key=word, class Hash=string::hash>
-struct HashTablePlusEqOp
-{
-    typedef HashTable<T, Key, Hash> value_type;
-
-    void operator()(value_type& a, const value_type& b) const
-    {
-        a += b;
-    }
-};
-
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-} // End namespace Foam
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-#endif
-
-// ************************************************************************* //