How to tell legends from axes in Matlab?

Question

The following stackoverflow qestion:

Matlab: How to obtain all the axes handles in a figure handle?

identifies how to get handles to all of the axes from a figure in Matlab. However, this list will also contain handles to legends, at least in R2008a, which appear to also be axes. How can I tell (programatically) the legends from the real plot axes in a vector of axes handles?

Answer 1

From linkaxes, the code you want is:

ax = findobj(gcf,'type','axes','-not','Tag','legend','-not','Tag','Colorbar');

This will return the handles of all the data axes in the current figure.

Answer 2

1) By default the Tag property of legend is 'Legend'. Of course, there is no promise that it is not changed.

 get(l)

 ....
 BusyAction: 'queue'
      HandleVisibility: 'on'
               HitTest: 'on'
         Interruptible: 'off'
              Selected: 'off'
    SelectionHighlight: 'on'
                   **Tag: 'legend'**
                  Type: 'axes'
         UIContextMenu: 200.0018
              UserData: [1x1 struct]

 ....

2) Another difference (which is more robust) is that regular axes do not have String property, but legends do. I am not sure whether there are other types of objects that also have String property. For example:

  plot(magic(3));legend('a','v','b');
  allAxesInFigure = findall(f,'type','axes')
  b = isprop(allAxesInFigure,'String')

You can verify it by calling:

get(gca,'String')
??? Error using ==> get
There is no 'String' property in the 'axes' class.

But on the other hand, for legends there is such a property. That is why it is more robust.

 plot(magic(3)); l = legend('a','b','c');
 get(l,'String')

ans = 'a' 'b' 'c'

3) I would recommend to solve this in a broader context. Just keep track of the legends and axes you create by storing their handles. That is, instead of coding like:

 plot(magic(3));
 legend('a','v','b');
 plot(magic(5));
 legend('a','v','b','c','d');

Code like this:

 p(1) = plot(magic(3));
 l(1) = legend('a','v','b');
 p(2) = plot(magic(5));
 l(2) = legend('a','v','b','c','d');

Answer 3

Just slightly modifying the code of my answer at the stackoverflow question you mentioned:

axesHandles = get(fig, 'Children');
classHandles = handle(axesHandles);
count = length(axesHandles);
isLegend = false(1, count);
for i = 1:count
    isLegend(i) = strcmp(class(classHandles(i)), 'scribe.legend') == 1;
end
legendHandles = axesHandles(isLegend);

Unfortunately, this solution depends on implementation details.