Question

I would like to plot a vertical line (I’d prefer any orientation, but I’d be happy with just vertical right now) with two-color dashes, say red-blue-red-blue-…

I know I could do it like this:

plot([1,1],[0,1],'r'),
hold on,
plot([1,1],[0,1],'--b')

However, since I need to be able to move the line, among others, it should only have a single handle. How could I do this?

EDIT
Thank you for your answers. I guess I should indeed give some more information.

I have some data that is classified into different parts. I want to be able to manually adjust the boundaries between classes. For this, I’m drawing vertical lines at the classification boundaries and use draggable to allow moving the lines.

For the boundary between the red and the blue class, I’d like to have a red/blue line.

plot(ones(10,1),linspace(0,1,10),'-bs','MarkerFaceColor','r','MarkerEdgeColor','none','linewidth',6)

is what I’m actually using at the moment. However, it’s not so pretty (if I want equal spacing, it becomes a real pain, and I want to give both colors the same weight), and I would like to have the possibility to use three colors (and not with marker edge and face being different, because it makes my eyes bleed).

Unfortunately, draggable does not allow me to use multiple handles, and grouping the lines with hggroup does not seem to create a draggable object.

cline looks like a promising approach, but rainbow colors won’t work for my application.

Answer 1

You can use the code you have, and just concatenate the handles from each line into a vector of handles. When you want to change the properties of both lines simultaneously, the SET function is able to accept the vector of handles as an argument. From the documentation for SET:

set(H,'PropertyName',PropertyValue,...)
sets the named properties to the
specified values on the object(s)
identified by H. H can be a vector of
handles, in which case set sets the
properties’ values for all the
objects.

Here’s an example:

h1 = plot([1 1],[0 1],'r');    %# Plot line 1
hold on;
h2 = plot([1 1],[0 1],'--b');  %# Plot line 2
hVector = [h1 h2];             %# Vector of handles
set(hVector,'XData',[2 3]);    %# Shifts the x data points for both lines

---

UPDATE: Since you mention you are using draggable from the MathWorks File Exchange, here’s an alternate solution. From the description of draggable:

A function which is called when the
object is moved can be provided as an
optional argument, so that the
movement triggers further actions.

You could then try the following solution:

• Plot your two lines, saving the handle for each (i.e. h1 and h2).

• Put the handle for each in the 'UserData' property of the other:

  set(h1,'UserData',h2);
  set(h2,'UserData',h1);
  

• Create the following function:

  function motionFcn(hMoving)  %# Currently moving handle is passed in
    hOther = get(hMoving,'UserData');  %# Get the other plot handle
    set(hOther,'XData',get(hMoving,'XData'),...  %# Update the x data
               'YData',get(hMoving,'YData'));    %# Update the y data
  end
  

• Turn on draggable for both lines, using the above function as the one called when either object is moved:

  draggable(h1,@motionFcn);
  draggable(h2,@motionFcn);