Removing the line between two specific data points in Matlab

Question

I am going to draw a graph in Matlab. The graph is quite simple and I am using the plot function. Suppose the data that I want to plot is (0:1:10). I also put markers on my graph. Then, we have a line that has markers on coordinates (0,0),(1,1),(2,2),... etc.

Now, I want to remove the line between (2,2) and (3,3) without deleting the whole line. That is to say, my purpose is to get rid of a particular segment of the line without loosing the entire line or any marker points.

How can I do that?

Answer 1

Removing the section of line after you have plotted it is difficult. You can see that the line is made up of one MATLAB object by the following code:

x = 1:10;
y = 1:10;
H = plot(x, y, '-o');
get(H, 'children')

ans =

Empty matrix: 0-by-1

We can see that the line has no children, so there are no 'subparts' that we can remove. However, there are some cheeky tricks we can use to try to achieve the same effect.

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Plot two lines separately

...using hold on. See Victor Hugo's answer. This is the proper way of achieving our goal.

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Plot two separate lines in one

MATLAB doesn'y plot points with a NaN value. By modifying the input vectors, you can make MATLAB skip a point to give the effect of a broken line:

x = [0 1 2 2 3 4 5 6 7 8 9];
y = [0 1 2 nan 3 4 5 6 7 8 9];
plot(x, y, '-o');

This is equivalent to plotting a line from [0, 0] to [2, 2], skipping the next point, then starting again at [3, 3] and continuing to [9, 9].

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'Erase' part of the line

This is the nastiest way of doing it, but is a cheap hack that could work if you can't be bothered with changing your input arrays. First plot the line:

x = 1:10; y = 1:10;
plot(x, y, '-o');

Now plot a white line over the part you wish to erase:

hold on
plot([2 3], [2 3], 'w');

As you can see, the result doesn't quite look right, and will respond badly if you try to do other things to the graph. In short, I wouldn't recommend this method but it might come in useful in desperate times!

Answer 2

Try the following:

y = [0.2751 0.2494 0.1480 0.2419 0.2385 0.1295 0.2346 0.1661 0.1111];
x = 1:numel(y);

plot(x(1:4), y(1:4), '-x')
hold
plot(x(5:end), y(5:end), '-x')