Fix bug in append method

The append method contains a bug when it appends to a legend that has
been permuted previously or if the parent axes children have been
sorted differently after the legend has been modified. Append assumes
the parent axes children are in the same order as the current legend
PlotChildren, which may not be the case. For example, after permuting
the legend entries, this order may have changed.

Author: erikhuizinga

legtools.m

@@ -53,15 +53,27 @@ function append(lh, newStrings)
 
             % To make sure we target the right axes, pull the legend's
             % PlotChildren and get their parent axes object
-            parentaxes = lh.PlotChildren(1).Parent;
-            
-            % Get line object handles
-            plothandles = flipud(parentaxes.Children); % Flip so order matches
-            
-            % Update legend with line object handles & new string array
-            newlegendstr = [lh.String newStrings]; % Need to generate this before adding new plot objects
-            lh.PlotChildren = plothandles;
-            lh.String = newlegendstr;
+            ax = lh.PlotChildren(1).Parent;
+            
+            % Get graphics object handles
+            axchildren = flip(ax.Children); % Flip so order matches
+            legchildren = lh.PlotChildren;
+            
+            % Sort the children of the future legend object in an order
+            % depending on current legend PlotChildren property, because
+            % this may not be in the same order as axchildren, e.g. after
+            % permuting the legend entries
+            [~,~,icurrent] = intersect(legchildren,axchildren,'stable');
+            [~,idiff] = setdiff(axchildren,legchildren,'stable');
+            ifuture = [icurrent;idiff];
+            axchildren = axchildren(ifuture);
+            
+            % Strings desired order for future legend
+            newstr = [lh.String, newStrings];
+            
+            % Update legend with graphics object handles & new string array
+            lh.PlotChildren = axchildren;
+            lh.String = newstr;
         end % of append method
 
         function permute(lh, order)