`bag_tree()`

is a way to generate a *specification* of a model
before fitting and allows the model to be created using
different packages in R. The main arguments for the
model are:

`cost_complexity`

: The cost/complexity parameter (a.k.a.`Cp`

) used by CART models (`rpart`

only).`tree_depth`

: The*maximum*depth of a tree (`rpart`

).`min_n`

: The minimum number of data points in a node that are required for the node to be split further.`class_cost`

: A cost value to asign to the class corresponding to the first factor level (for 2-class models,`rpart`

and`C5.0`

only).

These arguments are converted to their specific names at the
time that the model is fit. Other options and argument can be
set using `set_engine()`

. If left to their defaults
here (`NULL`

), the values are taken from the underlying model
functions. If parameters need to be modified, `update()`

can be used
in lieu of recreating the object from scratch.

bag_tree( mode = "unknown", cost_complexity = 0, tree_depth = NULL, min_n = 2, class_cost = NULL ) # S3 method for bag_tree update( object, parameters = NULL, cost_complexity = NULL, tree_depth = NULL, min_n = NULL, class_cost = NULL, fresh = FALSE, ... )

mode | A single character string for the type of model. Possible values for this model are "unknown", "regression", or "classification". |
---|---|

cost_complexity | A positive number for the the cost/complexity
parameter (a.k.a. |

tree_depth | An integer for maximum depth of the tree. |

min_n | An integer for the minimum number of data points in a node that are required for the node to be split further. |

class_cost | A non-negative scalar for a class cost (where a cost of 1 means no extra cost). This is useful for when the first level of the outcome factor is the minority class. If this is not the case, values between zero and one can be used to bias to the second level of the factor. |

object | A bagged tree model specification. |

parameters | A 1-row tibble or named list with |

fresh | A logical for whether the arguments should be modified in-place of or replaced wholesale. |

... | Not used for |

The model can be created using the `fit()`

function using the
following *engines*:

R:

`"rpart"`

(the default) or`"C5.0"`

(classification only)

Note that, for `rpart`

models, but `cost_complexity`

and
`tree_depth`

can be both be specified but the package will give
precedence to `cost_complexity`

. Also, `tree_depth`

values
greater than 30 `rpart`

will give nonsense results on 32-bit
machines.

library(parsnip) set.seed(9952) bag_tree(tree_depth = 5) %>% set_mode("classification") %>% set_engine("rpart", times = 3) %>% fit(Species ~ ., data = iris)#> parsnip model object #> #> Fit time: 615ms #> Bagged CART (classification with 3 members) #> #> Variable importance scores include: #> #> # A tibble: 4 x 4 #> term value std.error used #> <chr> <dbl> <dbl> <int> #> 1 Petal.Length 88.9 1.05 3 #> 2 Petal.Width 88.5 2.78 3 #> 3 Sepal.Length 65.4 3.08 3 #> 4 Sepal.Width 44.8 2.01 3 #>model <- bag_tree(cost_complexity = 10, min_n = 3) model#> Bagged Decision Tree Model Specification (unknown) #> #> Main Arguments: #> cost_complexity = 10 #> min_n = 3 #>#> Bagged Decision Tree Model Specification (unknown) #> #> Main Arguments: #> cost_complexity = 1 #> min_n = 3 #>#> Bagged Decision Tree Model Specification (unknown) #> #> Main Arguments: #> cost_complexity = 1 #>