lasso.m

Posted by Robert Bemis, September 25, 2009

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Bob's pick this week is lasso.m by Thomas Rutten.

Suppose you have a set of XY points. You plot them to see how they spread out. You decide a certain clump of points is special. How do you get MATLAB to know which points you care about? With lasso you can select them with your mouse!

To demonstrate I will use the sunspot example data that ships with MATLAB.

load sunspot.dat
[x,y,i] = lasso(sunspot(:,1),sunspot(:,2))

press a KEY to start selection by mouse, LEFT mouse button for selection, RIGHT button closes loop
x =
        1836
        1837
        1848
        1870
y =
        121.5
        138.3
        124.7
          139
i =
   137
   138
   149
   171

centroid = [mean(x) mean(y)]

centroid =
       1847.8       130.88

The program prompted me how to start and stop the selection. I left off the semicolon to show the values returned for further analysis (ie, centroid calculation). The first plot shows the polygon region I selected. The second plot shows the selected points with a free legend and point counter. Nice!

Note: if you like graphically interacting with your XY points be sure to check out Data Brushing introduced with R2008a.

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Published with MATLAB® 7.9