How do I extract data points from a plot?

I would like to extract data points from a plot.

Answer 1

[MathWorks Support Team]

You can get the data from a plot by accessing the XData and YData properties from each Line object in the axes.  

1. Make the figure containing the plot the current figure. An easy way to do this is to click the figure to bring it to the foreground. 

2. Call the gca command to get the current axes within that figure. Then pass the axes to the findobj function to search for all lines in the axes. For example, here is a plot containing one line.

figure
plot([1 2])
ax = gca; 
h = findobj(gca,'Type','line');

3. Get the coordinates from the XData and YData properties of the Line object.  

x = h.XData; 
y = h.YData;

If the plot has multiple lines, h is returned as an array of Line objects. Use array indexing to access each Line object in h. Then you can get the XData and YData properties from each Line object.

For example, here’s a plot containing three lines.

figure 
plot([1 2 3; 4 5 6]) 
ax = gca; 
h = findobj(gca,'Type','line'); 

x1 = h(1).XData; 
y1 = h(2).YData; 

x2 = h(2).XData; 
y2 = h(1).YData; 

x3 = h(3).XData; 
y3 = h(3).YData;

[Walter Roberson]

Suppose you have two graphics objects h1 and h2, both of them with increasing X values, but the X values might not be exactly the same. For example, the second X series might be roughly 3 milliseconds after the first X series because of time spent acquiring the data.

In such a case, to align the data values:

x1 = h1.XData;
y1 = h1.YData;
x2 = h2.XData;
y2 = h2.YData;
y2aligned = interp1(x2, y2, x1, 'linear', 'extrap');

Now you have

x1 -- used for both sets of data
y1 -- y for the first set of data
y2aligned -- y for the second set of data, calculated at common time x1