1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
|
% $Id: dbApply.Rd,v d0.1 2008/08/10 18:04:01 psk Exp $
\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{PostgreSQL}} driver implements a method
(see the helper function \code{\link{postgresqlDBApply}}) for this
generic function.
}
\value{
A list with as many elements as there were groups in the
result set.
}
\seealso{
\code{\link{PostgreSQL}}
\code{\link{postgresqlDBApply}}
\code{\link[DBI]{dbSendQuery}}
\code{\link[DBI]{fetch}}
}
\examples{\dontrun{
## compute quantiles for each network agent
con <- dbConnect(PostgreSQL(), user= "user", password="passwd", dbname="sample")
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
|
