blackboost {mboost} | R Documentation

## Gradient Boosting with Regression Trees

### Description

Gradient boosting for optimizing arbitrary loss functions where regression trees are utilized as base-learners.

### Usage

    blackboost(formula, data = list(),
               weights = NULL, na.action = na.pass,
               offset = NULL, family = Gaussian(),
               control = boost_control(),
               oobweights = NULL,
               tree_controls = party::ctree_control(
                   teststat = "max",
                   testtype = "Teststatistic",
                   mincriterion = 0,
                   maxdepth = 2, savesplitstats = FALSE),
               ...)

### Arguments

`formula` | a symbolic description of the model to be fit.
`data` | a data frame containing the variables in the model.
`weights` | an optional vector of weights to be used in the fitting process.
`na.action` | a function which indicates what should happen when the data contain `NA`s.
`offset` | a numeric vector to be used as offset (optional).
`family` | a `Family` object.
`control` | a list of parameters controlling the algorithm. For more details see `boost_control`.
`oobweights` | an additional vector of out-of-bag weights, which is used for the out-of-bag risk (i.e., if `boost_control(risk = "oobag")`). This argument is also used internally by `cvrisk`.
`tree_controls` | an object of class `"TreeControl"`, which can be obtained using `ctree_control`. Defines hyper-parameters for the trees which are used as base-learners. It is wise to make sure to understand the consequences of altering any of its arguments.
`...` | additional arguments passed to `mboost_fit`, including `weights`, `offset`, `family` and `control`. For default values see `mboost_fit`.

### Details

This function implements the ‘classical’ gradient boosting utilizing regression trees as base-learners. Essentially, the same algorithm is implemented in package `gbm`. The main difference is that arbitrary loss functions to be optimized can be specified via the `family` argument to `blackboost` whereas `gbm` uses hard-coded loss functions. Moreover, the base-learners (conditional inference trees, see `ctree`) are a little bit more flexible.

The regression fit is a black box prediction machine and thus hardly interpretable.

Partial dependency plots are not yet available; see example section for plotting of additive tree models.

### Value

An object of class `mboost` with `print` and `predict` methods being available.

### References

Peter Buehlmann and Torsten Hothorn (2007), Boosting algorithms: regularization, prediction and model fitting. Statistical Science, 22(4), 477–505.

Torsten Hothorn, Kurt Hornik and Achim Zeileis (2006). Unbiased recursive partitioning: A conditional inference framework. Journal of Computational and Graphical Statistics, 15(3), 651–674.

Yoav Freund and Robert E. Schapire (1996), Experiments with a new boosting algorithm. In Machine Learning: Proc. Thirteenth International Conference, 148–156.

Jerome H. Friedman (2001), Greedy function approximation: A gradient boosting machine. The Annals of Statistics, 29, 1189–1232.

Greg Ridgeway (1999), The state of boosting. Computing Science and Statistics, 31, 172–181.

### See Also

See `mboost_fit` for the generic boosting function, `glmboost` for boosted linear models, and `gamboost` for boosted additive models.

See `baselearners` for possible base-learners.

See `cvrisk` for cross-validated stopping iteration.

Furthermore see `boost_control`, `Family` and `methods`.

### Examples

    ### a simple two-dimensional example: cars data
    cars.gb <- blackboost(dist ~ speed, data = cars,
                          control = boost_control(mstop = 50))
    cars.gb

    ### plot fit
    plot(dist ~ speed, data = cars)
    lines(cars$speed, predict(cars.gb), col = "red")

    ############################################################
    ## Do not run this example automatically as it takes
    ## some time (~ 5-10 seconds depending on the system)

    ### set up and plot additive tree model
    if (require("party")) {
        ctrl <- ctree_control(maxdepth = 3)
        viris <- subset(iris, Species != "setosa")
        viris$Species <- viris$Species[, drop = TRUE]
        imod <- mboost(Species ~ btree(Sepal.Length, tree_controls = ctrl) +
                                 btree(Sepal.Width, tree_controls = ctrl) +
                                 btree(Petal.Length, tree_controls = ctrl) +
                                 btree(Petal.Width, tree_controls = ctrl),
                       data = viris, family = Binomial())[500]
        layout(matrix(1:4, ncol = 2))
        plot(imod)
    }

[Package mboost version 2.8-1 Index]