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\name{aggregator}
\docType{class}
\alias{class:aggregator}
\alias{aggregator}
\alias{aggregator-class}
\alias{initialize,aggregator-method}
\alias{aggenv,aggregator-method}
\alias{aggfun,aggregator-method}
\alias{initfun,aggregator-method}
\concept{aggenv}
\concept{aggfun}
\concept{initfun}
\title{A Simple Class for Aggregators }
\description{ A class of objects designed to help aggregate
calculations over an iterative computation. The aggregator consists
of three objects. An environment to hold the values.
A function that sets up an initial value the first time an object is
seen. An aggregate function that increments the value of an object
seen previously. }
\section{Creating Objects}{
\code{new('aggregator', aggenv = [environment], initfun = [function], aggfun = [function])}
}
\section{Slots}{
\describe{
\item{\code{aggenv}:}{Object of class 'environment', holds the values between iterations}
\item{\code{initfun}:}{Object of class 'function' specifies how to initialize the value for a name the first time it is encountered}
\item{\code{aggfun}:}{Object of class 'function' used to increment (or perform any other function) on a name}
}
}
\section{Methods}{
\describe{
\item{\code{aggenv(aggregator)}:}{Used to access the environment of the aggregator}
\item{\code{aggfun(aggregator)}:}{Used to access the function that aggregates}
\item{\code{initfun(aggregator)}:}{Used to access the initializer function}
}
}
\seealso{
\code{\link{Aggregate}}
}
\details{
This class is used to help aggregate different values over function
calls. A very simple example is to use leave one out cross-validation
for prediction. At each stage we first perform feature selection and
then cross-validate. To keep track of how often each feature is
selected we can use an aggregator. At the end of the cross-validation
we can extract the names of the features chosen from \code{aggenv}.
}
\keyword{methods}
\keyword{classes}
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