What predictor variables are used for a given pruning level in a classregtree?

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I'm working with classification and regression trees - I can define them, prune them, and even view the pruned tree with the predictor variable names displayed using the view() function. However, for an optimally pruned tree, I want to know which of the 6 predictor variables are actually being used. I can see this in the view(Tree) display, but I need some sort of index to be returned in my code, so I don't have to manually open a tree, assess the variables, and store which ones ended up being significant every time. Is there a way to do this?
To reiterate - for a classregtree and a given pruning level, how can I extract the predictor variables (either a name or index) that are being used? My optimally pruned trees tend to disregard at least one of my 6 predictor variables, and I want to know which are actually used without manually viewing the tree.
I'm using Matlab 7.12.0.635 win64 Thank you very much!

Accepted Answer

Ilya
Ilya on 28 Oct 2013
Prune the tree to the desired level using the prune method. Then use the cutvar method to see what variables are used for splits in each node. For example:
load ionosphere
t = classregtree(X,Y);
t = prune(t,'level',3);
varsUsedInTree = ismember(names(t),cutvar(t)')
Typing methods(t) or looking at the classregtree doc would give you a full list of methods.
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