Updating data cursor position within a loop - matlab

Question

I have a function updating a plot given a new point (it appends the last point to the line). I want to have the possibility to update the cursor such that it automatically appears on the last point. Currently, I do
for i = 1 : numel(dataObjs)
X{i}(end+1) = newX{i};
Y{i}(end+1) = newY{i};
set(dataObjs(i), 'XData', X{i});
set(dataObjs(i), 'YData', Y{i});
set(cursorMode, 'enable', 'on');
% Create a new data tip
hDatatip = cursorMode.createDatatip(dataObjs(i));
% Update annotation position
hDatatip.Cursor.Position = [newX{i}, newY{i} 0];
end
However, it is slow since it always creates a new cursor. I cannot find where the old one is stored such that I don't have to create new ones.

Answer 1

Rather than creating a new cursor object every time you add new data, you could create it once (per plot object) and save it to a variable. Then inside of the loop you can update the position.
set(cursorMode, 'Enable', 'on')
%// Create all of your data cursors once
for k = 1:numel(dataObjs)
datacursors(k) = cursorMode.createDatatip(dataObjs(k));
end
%// Now when you add new data
for k = 1 : numel(dataObjs)
X{k}(end+1) = newX{k};
Y{k}(end+1) = newY{k};
set(dataObjs(k), 'XData', X{k});
set(dataObjs(k), 'YData', Y{k});
%// Update annotation position
datacursors(k).Cursor.Position = [newX{k}, newY{k} 0];
end
And for the sake of a complete example:
hfig = figure();
data = rand(5,4);
hplots = plot(data);
cursorMode = datacursormode(hfig);
for k = 1:numel(hplots)
datacursors(k) = cursorMode.createDatatip(hplots(k));
end
for k = 1:size(data, 1)
for m = 1:numel(hplots)
set(datacursors(m), 'Position', [k, data(k,m)])
end
end
Update
As an alternative you could use findall to actually locate the data cursor for a given plot. The only downside of this is that it adds the overhead of having to find the data cursor every time that you want to update it.
datacursor = findall(ancestor(hplots(k), 'axes'), 'DataSource', hplots(k));
Another alternative
Rather than storing everything within a variable, you could store the data cursor in the UserData property of the plot objects themselves.
for k = 1:numel(hplots)
set(hplots(k), 'UserData', cursorMode.createDatatip(hplots(k)))
end
Then to use it:
set(get(hplots(k), 'UserData'), 'Position', [x, y, 0])