Predict resubstitution response of tree
label = resubPredict(tree)
[label,posterior] = resubPredict(tree)
[label,posterior,node] = resubPredict(tree)
[label,posterior,node,cnum] = resubPredict(tree)
[label,...] = resubPredict(tree,Name,Value)
A classification tree constructed by
comma-separated pairs of
the argument name and
Value is the corresponding value.
Name must appear inside single quotes (
' '). You can
specify several name and value pair arguments in any order as
Matrix or array of posterior probabilities for classes
The node numbers of
The class numbers that
Find the total number of misclassifications of the Fisher iris data for a classification tree.
load fisheriris tree = fitctree(meas,species); Ypredict = resubPredict(tree); % The predictions Ysame = strcmp(Ypredict,species); % True when == sum(~Ysame) % How many are different?
ans = 3
Load Fisher's iris data set. Partition the data into training (50%)
Grow a classification tree using the all petal measurements.
Mdl = fitctree(meas(:,3:4),species); n = size(meas,1); % Sample size K = numel(Mdl.ClassNames); % Number of classes
View the classification tree.
The classification tree has four pruning levels. Level 0 is the full, unpruned tree (as displayed). Level 4 is just the root node (i.e., no splits).
Estimate the posterior probabilities for each class using the subtrees pruned to levels 1 and 3.
[~,Posterior] = resubPredict(Mdl,'SubTrees',[1 3]);
Posterior is an
K-by- 2 array of posterior probabilities. Rows of
Posterior correspond to observations, columns correspond to the classes with order
Mdl.ClassNames, and pages correspond to pruning level.
Display the class posterior probabilities for iris 125 using each subtree.
ans(:,:,1) = 0 0.0217 0.9783 ans(:,:,2) = 0 0.5000 0.5000
The decision stump (page 2 of
Posterior) has trouble predicting whether iris 125 is versicolor or virginica.
The posterior probability of the classification at a node is the number of training sequences that lead to that node with this classification, divided by the number of training sequences that lead to that node.
For example, consider classifying a predictor
X is false otherwise.
Generate 100 random points and classify them:
rng(0) % For reproducibility X = rand(100,1); Y = (abs(X - .55) > .4); tree = fitctree(X,Y); view(tree,'Mode','graph')
Prune the tree:
tree1 = prune(tree,'Level',1); view(tree1,'Mode','graph')
The pruned tree correctly classifies observations
that are less than 0.15 as
true. It also correctly
classifies observations between .15 and .94 as
However, it incorrectly classifies observations that are greater than
false. Therefore the score for observations
that are greater than .15 should be about .05/.85=.06 for
and about .8/.85=.94 for
Compute the prediction scores for the first 10 rows of
[~,score] = predict(tree1,X(1:10)); [score X(1:10,:)]
ans = 0.9059 0.0941 0.8147 0.9059 0.0941 0.9058 0 1.0000 0.1270 0.9059 0.0941 0.9134 0.9059 0.0941 0.6324 0 1.0000 0.0975 0.9059 0.0941 0.2785 0.9059 0.0941 0.5469 0.9059 0.0941 0.9575 0.9059 0.0941 0.9649
every value of
X (the rightmost column) that is
less than 0.15 has associated scores (the left and center columns)
1, while the other
X have associated scores of