Bootstrap aggregation for ensemble of decision trees
TreeBagger
bags an ensemble of decision trees
for either classification or regression. Bagging stands for bootstrap
aggregation. Every tree in the ensemble is grown on an independently
drawn bootstrap replica of input data. Observations not included in
this replica are "out of bag" for this tree. To compute prediction
of an ensemble of trees for unseen data, TreeBagger
takes
an average of predictions from individual trees. To estimate the prediction
error of the bagged ensemble, you can compute predictions for each
tree on its outofbag observations, average these predictions over
the entire ensemble for each observation and then compare the predicted
outofbag response with the true value at this observation.
TreeBagger
relies on the ClassificationTree
and RegressionTree
functionality
for growing individual trees. In particular, ClassificationTree
and RegressionTree
accepts
the number of features selected at random for each decision split
as an optional input argument.
The compact
method returns an object of another
class, CompactTreeBagger
, with sufficient information
to make predictions using new data. This information includes the
tree ensemble, variable names, and class names (for classification). CompactTreeBagger
requires
less memory than TreeBagger
, but only TreeBagger
has
methods for growing more trees for the ensemble. Once you grow an
ensemble of trees using TreeBagger
and no longer
need access to the training data, you can opt to work with the compact
version of the trained ensemble from then on.
TreeBagger  Create ensemble of bagged decision trees 
append  Append new trees to ensemble 
compact  Compact ensemble of decision trees 
error  Error (misclassification probability or MSE) 
fillProximities  Proximity matrix for training data 
growTrees  Train additional trees and add to ensemble 
margin  Classification margin 
mdsProx  Multidimensional scaling of proximity matrix 
meanMargin  Mean classification margin 
oobError  Outofbag error 
oobMargin  Outofbag margins 
oobMeanMargin  Outofbag mean margins 
oobPredict  Ensemble predictions for outofbag observations 
predict  Predict response 

A cell array containing the class names for the response variable 

A logical flag specifying whether outofbag predictions for
training observations should be computed. The default is If this flag is true, the following properties are available:
If this flag is true, the following methods can be called:
See also 

A logical flag specifying whether outofbag estimates of variable
importance should be computed. The default is If this flag is


Square matrix, where This property is:


Default value returned by


A numeric array of size 1byNvars of changes in the split criterion summed over splits on each variable, averaged across the entire ensemble of grown trees. See also 

Fraction of observations that are randomly selected with replacement
for each bootstrap replica. The size of each replica is Nobs× 

A logical flag specifying whether decision tree leaves with
the same parent are merged for splits that do not decrease the total
risk. The default value is 

Method used by trees. The possible values are 

Minimum number of observations per tree leaf. By default, 

Scalar value equal to the number of decision trees in the ensemble. 

A numeric array of size 1byNvars, where every element gives a number of splits on this predictor summed over all trees. 

Number of predictor or feature variables to select at random
for each decision split. By default, 

Logical array of size NobsbyNTrees,
where Nobs is the number of observations in the
training data and NTrees is the number of trees
in the ensemble. A 

Numeric array of size Nobsby1 containing the number of trees used for computing the outofbag response for each observation. Nobs is the number of observations in the training data used to create the ensemble. 

A numeric array of size 1byNvars containing a measure of variable importance for each predictor variable (feature). For any variable, the measure is the difference between the number of raised margins and the number of lowered margins if the values of that variable are permuted across the outofbag observations. This measure is computed for every tree, then averaged over the entire ensemble and divided by the standard deviation over the entire ensemble. This property is empty for regression trees. 

A numeric array of size 1byNvars containing a measure of importance for each predictor variable (feature). For any variable, the measure is the increase in prediction error if the values of that variable are permuted across the outofbag observations. This measure is computed for every tree, then averaged over the entire ensemble and divided by the standard deviation over the entire ensemble. 

A numeric array of size 1byNvars containing a measure of importance for each predictor variable (feature). For any variable, the measure is the decrease in the classification margin if the values of that variable are permuted across the outofbag observations. This measure is computed for every tree, then averaged over the entire ensemble and divided by the standard deviation over the entire ensemble. This property is empty for regression trees. 

A numeric array of size Nobsby1, where Nobs is the number of observations in the training data, containing outlier measures for each observation. See also 

Numeric vector of prior probabilities for each class. The order
of the elements of This property is:


A numeric matrix of size NobsbyNobs, where Nobs is the number of observations in the training data, containing measures of the proximity between observations. For any two observations, their proximity is defined as the fraction of trees for which these observations land on the same leaf. This is a symmetric matrix with 1s on the diagonal and offdiagonal elements ranging from 0 to 1. See also 

The See also 

A logical flag specifying if data are sampled for each decision
tree with replacement. True if 

Cell array of arguments for 

A cell array of size NTreesby1 containing the trees in the ensemble. See also 

A matrix of size NvarsbyNvars with
predictive measures of variable association, averaged across the entire
ensemble of grown trees. If you grew the ensemble setting 

A cell array containing the names of the predictor variables
(features). 

Numeric vector of weights of length Nobs,
where Nobs is the number of observations (rows)
in the training data. 

A numeric matrix of size NobsbyNvars, where Nobs is the number of observations (rows) and Nvars is the number of variables (columns) in the training data. This matrix contains the predictor (or feature) values. 

An array of true class labels for classification, or response
values for regression. 
Value. To learn how this affects your use of the class, see Comparing Handle and Value Classes in the MATLAB^{®} ObjectOriented Programming documentation.