Allow option label to be a date index

Overlap/plot_traj.py

@@ -106,8 +106,8 @@ if __name__ == "__main__":
     parser.add_argument("shpc_dir", help = "directory containing SHPC, with "
                         "visible eddies at all dates")
     parser.add_argument("-l", "--label",
-                        choices = ["root", "leaf", "split", "merge", "all",
-                                   "important"])
+                        help = '"root", "leaf", "split", "merge", "all", '
+                        '"important" or integer for date index')
     parser.add_argument("-s", "--save", metavar = "format",
                         help = "Save file to specified format")
     parser.add_argument("-t", "--time", action = "store_true",
@@ -120,6 +120,10 @@ if __name__ == "__main__":
                        metavar = ("lllon", "lllat", "urlon", "urlat"))
     args = parser.parse_args()
 
+    if args.label not in {None, "root", "leaf", "split", "merge", "all",
+                          "important"}:
+        args.label = int(args.label)
+
     plt.figure()
 
     if args.window is not None: