R-callbacks docs

R-package/man/callbacks.Rd

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+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/callbacks.R
+\name{callbacks}
+\alias{callbacks}
+\title{Callback closures for booster training.}
+\description{
+These are used to perform various service tasks either during boosting iterations or at the end.
+This approach helps to modularize many of such tasks without bloating the main training methods, 
+and it offers .
+}
+\details{
+By default, a callback function is run after each boosting iteration.
+An R-attribute \code{is_pre_iteration} could be set for a callback to define a pre-iteration function.
+
+When a callback function has \code{finalize} parameter, its finalizer part will also be run after 
+the boosting is completed.
+
+WARNING: side-effects!!! Be aware that these callback functions access and modify things in 
+the environment from which they are called from, which is a fairly uncommon thing to do in R.
+
+To write a custom callback closure, make sure you first understand the main concepts about R envoronments.
+Check either the R docs on \code{\link[base]{environment}} or the 
+\href{http://adv-r.had.co.nz/Environments.html}{Environments chapter} from Hadley Wickham's "Advanced R" book.
+Then take a look at the code of \code{cb.reset_learning_rate} for a simple example, 
+and see the \code{cb.log_evaluation} code for something more involved.
+Also, you would need to get familiar with the objects available inside of the \code{xgb.train} internal environment.
+}
+\seealso{
+\code{\link{cb.print_evaluation}},
+\code{\link{cb.log_evaluation}},
+\code{\link{cb.reset_parameters}},
+\code{\link{cb.early_stop}},
+\code{\link{cb.save_model}},
+\code{\link{xgb.train}},
+\code{\link{xgb.cv}}
+}
+