add group::assign convenience version

src/group.cpp

@@ -547,6 +547,22 @@ void Group::assign(int narg, char **arg)
   }
 }
 
+/* ----------------------------------------------------------------------
+   convenience function to allow assigning to groups from a single string
+------------------------------------------------------------------------- */
+
+void Group::assign(const std::string &fixcmd)
+{
+  std::vector<std::string> args = utils::split_words(fixcmd);
+  char **newarg = new char*[args.size()];
+  int i=0;
+  for (const auto &arg : args) {
+    newarg[i++] = (char *)arg.c_str();
+  }
+  assign(args.size(),newarg);
+  delete[] newarg;
+}
+
 /* ----------------------------------------------------------------------
    add flagged atoms to a new or existing group
 ------------------------------------------------------------------------- */

src/group.h

@@ -30,6 +30,7 @@ class Group : protected Pointers {
   Group(class LAMMPS *);
   ~Group();
   void assign(int, char **);         // assign atoms to a group
+  void assign(const std::string &);  // convenience function
   void create(char *, int *);        // add flagged atoms to a group
   int find(const char *);            // lookup name in list of groups
   int find_or_create(const char *);  // lookup name or create new group