ENH: add 'use' action for parcel selection

- shortcut for "clear" + "add".

  At the end of the operation, only parcels matching that particular
  selection source will be used.

src/functionObjects/lagrangian/common/parcelSelectionDetail.C

@@ -41,6 +41,7 @@ Foam::Detail::parcelSelection::actionNames
     { actionType::ALL, "all" },
     { actionType::CLEAR, "clear" },
     { actionType::INVERT, "invert" },
+    { actionType::USE, "use" },
     { actionType::ADD, "add" },
     { actionType::SUBTRACT, "subtract" },
     { actionType::SUBSET, "subset" },
@@ -90,7 +91,14 @@ namespace Foam
         switch (action)
         {
             case actionType::ADD:
+            case actionType::USE:
             {
+                if (actionType::USE == action)
+                {
+                    // USE = CLEAR + ADD  (ie, only use this selection)
+                    selection = false;
+                }
+
                 for (label parceli = 0; parceli < len; ++parceli)
                 {
                     if (accept(aop(list[parceli])))

src/functionObjects/lagrangian/common/parcelSelectionDetail.H

@@ -35,7 +35,7 @@ Description
         stride
         {
             // every 10th parcelId
-            action  add;
+            action  use;
             source  stride;
             stride  10;
         }
@@ -69,7 +69,7 @@ Description
     \heading Entry type
     \table
         Property    | Description                           | Required | Default
-        action      | all/clear/invert add/subtract/subset/ignore | yes |
+        action      | all/clear/invert/ignore add/subtract/subset/use | yes |
         source      | field/stride                          | mostly  |
     \endtable
 
@@ -149,6 +149,7 @@ public:
         ADD,                //!< "add" - parcel selection
         SUBTRACT,           //!< "subtract" - remove parcel selection
         SUBSET,             //!< "subset" - subset parcel selection
+        USE,                //!< "use" - same as clear + add
         IGNORE,             //!< "ignore" - dummy no-op
     };
 

tutorials/lagrangian/reactingParcelFoam/filter/system/dataCloud

@@ -23,7 +23,7 @@ dataCloud
         // Reduced number of output parcels
         stride
         {
-            action  add;
+            action  use;
             source  stride;
             stride  4;
         }