TreeBagger class
Bag of decision trees
Description
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.
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. That is, TreeBagger
implements the random forest algorithm [1].
For regression problems, TreeBagger
supports mean and quantile regression (that is, quantile regression forest [2]).
To predict mean responses or estimate the meansquared error given data, pass a
TreeBagger
model and the data topredict
orerror
, respectively. To perform similar operations for outofbag observations, useoobPredict
oroobError
.To estimate quantiles of the response distribution or the quantile error given data, pass a
TreeBagger
model and the data toquantilePredict
orquantileError
, respectively. To perform similar operations for outofbag observations, useoobQuantilePredict
oroobQuantileError
.
Construction
TreeBagger  Create bag of decision trees 
Object Functions
append  Append new trees to ensemble 
compact  Compact ensemble of decision trees 
error  Error (misclassification probability or MSE) 
fillprox  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 
oobQuantileError  Outofbag quantile loss of bag of regression trees 
oobQuantilePredict  Quantile predictions for outofbag observations from bag of regression trees 
partialDependence  Compute partial dependence 
plotPartialDependence  Create partial dependence plot (PDP) and individual conditional expectation (ICE) plots 
predict  Predict responses using ensemble of bagged decision trees 
quantileError  Quantile loss using bag of regression trees 
quantilePredict  Predict response quantile using bag of regression trees 
Properties

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
If this flag is


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. 

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 NobsbyNumTrees, where Nobs is the number of observations in the training data and NumTrees 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. 

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. 

The 

A logical flag specifying if data are sampled for each decision tree with replacement. This property is 

Cell array of arguments for 

A cell array of size NumTreesby1 containing the trees in the ensemble. 

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 table or 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. If you train the ensemble using a table of predictor values, then 

A size Nobs array of response data. Elements of 
Examples
Copy Semantics
Value. To learn how this affects your use of the class, see Comparing Handle and Value Classes in the MATLAB^{®} ObjectOriented Programming documentation.
Tips
For a TreeBagger
model object B
, the Trees
property stores a cell vector of B.NumTrees
CompactClassificationTree
or CompactRegressionTree
model objects. For a textual or graphical display of tree t
in the cell vector, enter
view(B.Trees{t})
Alternative Functionality
Statistics and Machine Learning Toolbox™ offers three objects for bagging and random forest:
ClassificationBaggedEnsemble
created byfitcensemble
for classificationRegressionBaggedEnsemble
created byfitrensemble
for regressionTreeBagger
created byTreeBagger
for classification and regression
For details about the differences between TreeBagger
and
bagged ensembles (ClassificationBaggedEnsemble
and
RegressionBaggedEnsemble
), see Comparison of TreeBagger and Bagged Ensembles.
References
[1] Breiman, L. "Random Forests." Machine Learning 45, pp. 5–32, 2001.
[2] Meinshausen, N. “Quantile Regression Forests.” Journal of Machine Learning Research, Vol. 7, 2006, pp. 983–999.
See Also
error
 oobError
 TreeBagger
 CompactTreeBagger
 compact
 view
 view
 oobPredict
 predict