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% $Id: dbApply.Rd 135 2003-12-02 14:53:01Z dj $
\name{dbApply}
\alias{dbApply}
\title{Apply R/S-Plus functions to remote groups of DBMS rows (experimental)}
\description{
Applies R/S-Plus functions to groups of remote DBMS rows without
bringing an entire result set all at once. The result set
is expected to be sorted by the grouping field.
}
\usage{
dbApply(res, ...)
}
\arguments{
\item{res}{a result set (see \code{\link[DBI]{dbSendQuery}}).}
\item{...}{any additional arguments to be passed to \code{FUN}.}
}
\details{
\code{dbApply}
This generic is meant to handle somewhat gracefully(?) large amounts
of data from the DBMS by bringing into R manageable chunks;
the idea is that the data from individual groups can be handled by R, but
not all the groups at the same time.
Currently, only the \code{\link{MySQL}} driver implements a method
(see the helper function \code{\link{mysqlDBApply}}) for this
generic function.
}
\value{
A list with as many elements as there were groups in the
result set.
}
\seealso{
\code{\link{MySQL}}
\code{\link{mysqlDBApply}}
\code{\link[DBI]{dbSendQuery}}
\code{\link[DBI]{fetch}}
}
\examples{\dontrun{
## compute quanitiles for each network agent
con <- dbConnect(MySQL(), group="vitalAnalysis")
rs <- dbSendQuery(con,
"select Agent, ip_addr, DATA from pseudo_data order by Agent")
out <- dbApply(rs, INDEX = "Agent",
FUN = function(x, grp) quantile(x$DATA, names=FALSE))
}
}
\keyword{programming}% at least one, from doc/KEYWORDS
\keyword{interface}% __ONLY ONE__ keyword per line
\keyword{database}
% vim: syntax=tex
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