ListOps: Added count function to return the number of occurrences of a value in a list

src/OpenFOAM/containers/Lists/ListOps/ListOps.H

@@ -168,6 +168,10 @@ List<OutList> invertManyToMany(const label len, const UList<InList>& in)
 //- Create identity map (map[i] == i) of given length
 labelList identity(const label len);
 
+//- Count the number of occurrences of a value in a list
+template<class ListType>
+label count(const ListType& l, typename ListType::const_reference x);
+
 //- Find first occurrence of given element and return index,
 //  return -1 if not found. Linear search.
 template<class ListType>

src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C

@@ -475,6 +475,25 @@ void Foam::invertManyToMany
 }
 
 
+template<class ListType>
+Foam::label Foam::count
+(
+    const ListType& l,
+    typename ListType::const_reference x
+)
+{
+    label result = 0;
+    forAll(l, i)
+    {
+        if (l[i] == x)
+        {
+            ++ result;
+        }
+    }
+    return result;
+}
+
+
 template<class ListType>
 Foam::label Foam::findIndex
 (