[R-gregmisc-users] SF.net SVN: r-gregmisc:[1506] trunk/gdata

[<wa...@us...>]

Revision: 1506
          http://r-gregmisc.svn.sourceforge.net/r-gregmisc/?rev=1506&view=rev
Author:   warnes
Date:     2011-09-20 18:07:07 +0000 (Tue, 20 Sep 2011)
Log Message:
-----------
Add case() function, a vector equivalent of the switch() function

Added Paths:
-----------
    trunk/gdata/R/case.R
    trunk/gdata/man/case.Rd

Added: trunk/gdata/R/case.R
===================================================================
--- trunk/gdata/R/case.R	                        (rev 0)
+++ trunk/gdata/R/case.R	2011-09-20 18:07:07 UTC (rev 1506)
@@ -0,0 +1,16 @@
+case <- function(x, ..., default=NA)
+{
+  magic <- "....default...."
+  alternatives <- c(...,"....default...."=magic)
+
+  x <- as.character(x)
+  retval <- factor(
+                   x,
+                   levels=alternatives,
+                   labels=names(alternatives)
+                   )
+  levels(retval)[length(alternatives)] <- as.character(default)  
+  retval[is.na(retval) & !is.na(x)] <- default
+
+  retval
+}

Added: trunk/gdata/man/case.Rd
===================================================================
--- trunk/gdata/man/case.Rd	                        (rev 0)
+++ trunk/gdata/man/case.Rd	2011-09-20 18:07:07 UTC (rev 1506)
@@ -0,0 +1,37 @@
+\name{case}
+\alias{case}
+\title{Map elements of a vector according to the provided 'cases'}
+\description{
+  Map elements of a vector according to the provided 'cases'.  This
+  function is useful for mapping discrete values to factor labels and 
+  is the vector equivalent to the \code{switch} function.
+}
+\usage{
+case(x, ..., default = NA)
+}
+\arguments{
+  \item{x}{Vector to be converted}
+  \item{\dots}{Map of alternatives, specified as "name"=value}
+  \item{default}{Value to be assigned to elements of \code{x} not
+    matching any of the alternatives. Defaults to \code{NA}.}
+}
+\details{
+  This function is to \code{switch} what \code{ifelse} is to \code{if},
+  and is a convenience wrapper for \code{factor}.
+}
+\value{
+  A factor variables with each element of \code{x} mapped into the
+  corresponding level of specified in the mapping.
+}
+\author{Gregory R. Warnes \email{gr...@wa...}}
+\seealso{\code{factor}, \code{switch}, \code{ifelse}}
+\examples{
+## default = NA
+case( c(1,1,4,3), "a"=1, "b"=2, "c"=3)
+
+## default = "foo"
+case( c(1,1,4,3), "a"=1, "b"=2, "c"=3, default="foo" )
+
+
+}
+\keyword{ manip }

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