Statistics Toolbox™

risk - Node risks

Class

@classregtree

Syntax

r = risk(t) r = risk(t,nodes)

Description

r = risk(t) returns an n-element vector r of the risk of the nodes in the tree t, where n is the number of nodes. The risk r(i) for node i is the node error e(i) (computed by nodeerr) weighted by the node probability p(i) (computed by nodeprob).

r = risk(t,nodes) takes a vector nodes of node numbers and returns the risk values for the specified nodes.

Example

Create a classification tree for Fisher's iris data:

load fisheriris;

t = classregtree(meas,species,...
                 'names',{'SL' 'SW' 'PL' 'PW'})
t = 
Decision tree for classification
1  if PL<2.45 then node 2 else node 3
2  class = setosa
3  if PW<1.75 then node 4 else node 5
4  if PL<4.95 then node 6 else node 7
5  class = virginica
6  if PW<1.65 then node 8 else node 9
7  class = virginica
8  class = versicolor
9  class = virginica

view(t)

e = nodeerr(t);
p = nodeprob(t);
r = risk(t);

r
r =
    0.6667
         0
    0.3333
    0.0333
    0.0067
    0.0067
    0.0133
         0
         0

e.*p
ans =
    0.6667
         0
    0.3333
    0.0333
    0.0067
    0.0067
    0.0133
         0
         0

Reference