It would be nice to have an option in XYgraph that could allow the user to define some set of spatially related points (or cluster in statistics) by drawing some boundaries with complex shapes using the mouse. Here is the problem that brought me to write this post. Let's say that we have a series of data {x1,x2...xi...xn} that represents the duration of time between two adjacent heart beats. The pointcare plot is the representation of the points [xi,x(i+1)] and that can be achieved to by the XYGraph function. Using this graphic, it is expected that adjacent intervals with almost similar values will form a cloud (circular, eliptic or with more complex shapes) centered around the average values of the xi. Now, unusual changes between adjacent xi values in the time series (lower or higher x(i+1)) will result in points outside of the primary cloud. This is an easy way to identify abrupt changes in a time series.
The step I'm blocked with the following. After I used the XY graph to plot the [Xi,X(i+1)], I would like to use the mouse the draw the border of the primary cloud and extract separately the indexes of the point in or points outside the border.
Again, I really appreciate your help for that.
Olivier
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