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\name{subset.data.table}
\alias{subset}
\alias{subset.data.table}
\title{ Subsetting data.tables }
\description{
Returns subsets of a \code{data.table}.
}
\usage{
\method{subset}{data.table}(x, subset, select, \ldots)
}
\arguments{
\item{x}{
\code{data.table} to subset.
}
\item{subset}{
logical expression indicating elements or rows to keep
}
\item{select}{
expression indicating columns to select from \code{data.table}
}
\item{\ldots}{
further arguments to be passed to or from other methods
}
}
\details{
The \code{subset} argument works on the rows and will be evaluated
in the \code{data.table} so columns can be referred to (by name) as variables
in the expression.
The \code{data.table} that is returned will maintain the original keys
as long as they are not \code{select}-ed out.
}
\value{
A \code{data.table} containing the subset of rows and columns that are
selected.
}
\seealso{ \code{\link[base]{subset}} }
\examples{
DT <- data.table(a=sample(c('a', 'b', 'c'), 20, replace=TRUE),
b=sample(c('a', 'b', 'c'), 20, replace=TRUE),
c=sample(20), key=c('a', 'b'))
sub <- subset(DT, a == 'a')
all.equal(key(sub), key(DT))
}
\keyword{ data }
|
