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\name{sets}
\alias{sets}
\alias{union}
\alias{intersect}
\alias{setdiff}
\title{Set operations}
\description{
Performs \emph{set} union, intersection and (asymmetric!) difference
on two vector-like objects.
NOTE: This man page is for the \code{union}, \code{intersect} and
\code{setdiff} \emph{S4 generic functions} defined in the \pkg{BiocGenerics}
package.
See \code{?base::\link[base]{union}} for the default methods
(defined in the \pkg{base} package).
Bioconductor packages can define specific methods for objects
(typically vector-like) not supported by the default methods.
}
\usage{
union(x, y, ...)
intersect(x, y, ...)
setdiff(x, y, ...)
}
\arguments{
\item{x, y}{
Vector-like objects (typically of the same class, but not necessarily).
}
\item{...}{
Additional arguments, for use in specific methods.
}
}
\value{
See \code{?base::\link[base]{union}} for the value returned by the
default methods.
Specific methods defined in Bioconductor packages will typically
return an object of the same class as the input objects.
}
\note{
The default methods (defined in the \pkg{base} package) only take 2
arguments. We've added the \code{...} argument to the generic functions
defined in the \pkg{BiocGenerics} package so they can be called with an
arbitrary number of effective arguments.
For \code{union} or \code{intersect}, this typically allows Bioconductor
packages to define methods that compute the union or intersection of more
than 2 objects. However, for \code{setdiff}, which is conceptually a
binary operation, this typically allows methods to add extra arguments
for controlling/altering the behavior of the operation.
Like for example the \code{ignore.strand} argument supported by the
\code{setdiff} method for \link[GenomicRanges]{GRanges} objects (defined
in the \pkg{GenomicRanges} package). (Note that the \code{union} and
\code{intersect} methods for those objects also support the
\code{ignore.strand} argument.)
}
\seealso{
\itemize{
\item \code{base::\link[base]{union}} for the default \code{union},
\code{intersect}, and \code{setdiff} methods.
\item \code{\link[methods]{showMethods}} for displaying a summary of the
methods defined for a given generic function.
\item \code{\link[methods]{selectMethod}} for getting the definition of
a specific method.
\item \link[GenomicRanges]{union,GRanges,GRanges-method} in the
\pkg{GenomicRanges} package for an example of a specific \code{union}
method (defined for \link[GenomicRanges]{GRanges} objects).
\item \link{BiocGenerics} for a summary of all the generics defined
in the \pkg{BiocGenerics} package.
}
}
\examples{
union
showMethods("union")
selectMethod("union", c("ANY", "ANY")) # the default method
intersect
showMethods("intersect")
selectMethod("intersect", c("ANY", "ANY")) # the default method
setdiff
showMethods("setdiff")
selectMethod("setdiff", c("ANY", "ANY")) # the default method
}
\keyword{methods}
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