Add function _get_isolated_buses

src/PlotUtils.jl

 #* Utility functions for various plotting functions
 #*------------------------------------------------------------------------------
 
-#= 
-Function for recursively merging two dictionaries (used for updating the dictionary containing plot settings).
-=#
-_recursive_merge(x::AbstractDict,y::AbstractDict) = merge(_recursive_merge,x,y)
-_recursive_merge(x,y) = y
-
 #=
 Returns the minimal and maximal values of bus longitude and latitude coordinates contained a dictionary. An offset can be used to arbitrarily increase the area.
 =#
@@ -28,6 +22,37 @@ function _get_pg_area(network_data::Dict{String,<:Any}, offset=0.)
     return _get_pg_area(pos, offset)
 end
 
+#*------------------------------------------------------------------------------
+
+#=
+Returns isolated buses that are not connected to any active branch.
+=#
+function _get_isolated_buses(network_data::Dict{String,<:Any})
+    ### Find buses connected to active branches
+    connected_buses = vcat(
+        [br["f_bus"] for br in values(network_data["branch"]) if 
+        br["br_status"] == 1],
+        [br["t_bus"] for br in values(network_data["branch"]) if 
+        br["br_status"] == 1]
+    )
+
+    ### Find isolated buses
+    isolated_buses = [
+        b["bus_i"] for b in values(network_data["bus"]) if 
+        b["bus_i"] ∉ connected_buses
+    ]
+
+    return unique(isolated_buses)
+end
+
+#*------------------------------------------------------------------------------
+
+#= 
+Function for recursively merging two dictionaries (used for updating the dictionary containing plot settings).
+=#
+_recursive_merge(x::AbstractDict,y::AbstractDict) = merge(_recursive_merge,x,y)
+_recursive_merge(x,y) = y
+
 #=
 Returns a dictionary of default plot settings for various plotting functions.
 =#
@@ -74,7 +99,8 @@ function _default_settings(func::Symbol)
                     "color" => "black",
                     "alpha" => 0.3,
                     "label" => "Empty buses",
-                    "show" => true
+                    "show" => true,
+                    "show_isolated" => false
                 )
             ),
             ### Settings for _draw_branches!