2

I want to plot a graph, mark a point and write legend in a loop.

labels = {}
for i = 1: size(error,1)
    r =  plot(handles.axes1,temp(i).time,temp(i).signal);
    hold (handles.axes1, 'on')
    a = %find minimum index 
    xmin = temp(i).time(a);
    ymin = temp(i).signal(a);
    plot(handles.axes1,xmin,ymin,'ro')
    labels{end+1} = sprintf('Type : %s, %f,%f',error{i,1}.main(1,1).type,xmin,ymin)
end

grid on
legend(r, labels);

Labeling does not work, as it takes only 1st elements ignoring extra element. and the whole method is a mess with color code all messed up, is there elegant way of doing this where my legend colour matches the plot ones

Suever
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Aashu10
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2 Answers2

4

Another way to do this is to use the DisplayName keyword.

for i = 1:N_lines
    %...
    r(i) = plot(handles.axes1, temp(i).time, temp(i).signal, 'DisplayName', labels{i});
    %...
end
legend('show')

The advantage of doing it like this is that it attaches the name directly to the plotted point. If you are debugging, and open the plot as its being written in the plot browser, as each point get plotted the name will appear next to the point in the right-hand pane. You also don't need to keep track of a separate labels variable in case you end up later reordering your points for some reason. This way the labels always travel with their associated points.

I should add that when you call the legend command with a cell of labels, among other things it backfills 'DisplayName' so that you can still change and query it after the plot has been built even if you don't explicitly set it like I've done above. However, I find this method to be self-documenting and more convenient because it's one less thing to keep track of.

craigim
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  • Nice approach and good explanation of its advantages. I've never noticed the DisplayName property in many many years of plotting. Thanks for the new trick! – b3. Aug 29 '16 at 16:57
  • I had to change my accepted answer to this, because this is more elegant and easy. – Aashu10 Aug 30 '16 at 08:30
3

You need to make r an array. As it is, you're only storing the last plot handle so when you call legend it's only going to use the last plot and the first label.

% Create a unique color for each plot
colors = hsv(size(error, 1));

for i = 1:size(error, 1)
    r(i) =  plot(handles.axes1,temp(i).time,temp(i).signal, 'Color', colors(i,:));
    %...
    labels{i} = sprintf('Type : %s, %f,%f',error{i,1}.main(1,1).type,xmin,ymin);
end

legend(r, labels)

As a side-note it's best to not use i or j as your looping variable and also, don't name your variable error as that's the name of a MATLAB built-in.

Suever
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  • I get not using error as a variable, but why not i or j as looping variable? – Aashu10 Aug 30 '16 at 06:22
  • `i` and `j` are [also functions](http://stackoverflow.com/questions/14790740/using-i-and-j-as-variables-in-matlab) – Suever Aug 30 '16 at 12:44