[Rd] new function: twotailed.colors {base}

[Wolfram Fischer - Z/I/M]

I suggest to add a new function to create a vector of
n ``contiguous'' colors with tails in two colors.
This function is similar to `cm.colors' but the colors
can be choosen by hsv values.

This function could be used e.g. as alternative to
the default ``col.regions'' in `levelplot'.

Perhaps the arguments in the following code could be 
simplified.

Wolfram Fischer

#--- twotailed.colors.R

twotailed.colors <-
function(
      n			= 7			# number of colors to be in the palette
	, n5		= n %% 2	# number of colors between the two tails
	, h1		= 0.02		# 0|1 = rot
	, h2		= 0.15		# 0.7 = blau, 0.15 = samtgelb, 0.35 = grün
	, s0		= 1			# saturation: begin and end
	, s5		= 1/n*1.4	# saturation: in the middle
	, v0		= 1			# value: begin and end
	, v5		= 1			# value: in the middle
	, s01		= s0		# beginning saturation of first tail
	, s02		= s0		# ending saturation of second tail
	, s51		= s5		# middle saturation on of first tail
	, s52		= s5		# middle saturation on of second tail
	, v01		= v0		# beginning value of first tail
	, v02		= v0		# ending value of second tail
	, v51		= v5		# middle value on of first tail
	, v52		= v5		# middle value on of second tail
	, n.tail	= ( n - n5 ) %/% 2
							# number of colors in each tail
	, s1		= seq( s01, s51, length = n.tail )
	, s2		= seq( s52, s02, length = n.tail )
	, v1		= seq( v01, v51, length = n.tail )
	, v2		= seq( v52, v02, length = n.tail )
){
	c(	hsv( h1, s1, v1 )
	,	rep( hsv( h1, round(s5,0), v5 ), n5 )
	,	hsv( h2, s2, v2 )
	)
}

#--- twotailed.colors.Rd

\name{twotailed.colors}
\alias{twotailed.colors}
\title{Two tailed color palette}
\description{
  Create a vector of \code{n} ``contiguous'' colors
  with tails in two colors.
}
\usage{
twotailed.colors( n = 7, n5 = n %% 2, h1 = 0.02, h2 = 0.15
	, s0 = 1, s5 = 1/n*1.4, v0 = 1, v5 = 1
	, s01 = s0, s02 = s0, s51 = s5, s52 = s5
	, v01 = v0, v02 = v0, v51 = v5, v52 = v5
	, n.tail = ( n - n5 ) %/% 2
	, s1 = seq( s01, s51, length = n.tail )
	, s2 = seq( s52, s02, length = n.tail )
	, v1 = seq( v01, v51, length = n.tail )
	, v2 = seq( v52, v02, length = n.tail )
	)
}
\arguments{
	\item{n}{ number of colors to be in the palette.}
	\item{n5}{ number of colors between the two tails.}
	\item{h1,h2}{values in the range \code{[0,1]} for the
		``hue'' of the color of each tail, e.g.:
		0 for red,
		0.15 for yellow,
		0.35 for green,
		0.7 for blue.}
	\item{s0}{ saturation: begin and end.}
	\item{s5}{ saturation: in the middle.}
	\item{v0}{ value: begin and end.}
	\item{v5}{ value: in the middle.}
	\item{s01}{ beginning saturation of the first tail.}
	\item{s02}{ ending saturation of the second tail.}
	\item{s51,s52}{ middle saturation on of the first and the second tail.}
	\item{v01}{ beginning value of the first tail.}
	\item{v02}{ ending value of the second tail.}
	\item{v51,v52}{ middle value on of the first and the second tail.}
	\item{n.tail}{ number of colors in each tail.}
	\item{s1,s2}{ vector of saturations of first and the second tail.}
	\item{v1,v2}{ vector of values of the first and the tail.}
}
\details{
}
\value{A character vector, \code{cv}, of color names.  This can be used
  either to create a user--defined color palette for subsequent
  graphics by \code{\link{palette}(cv)}, a \code{col=} specification
  in graphics functions or in \code{par}.
}
\seealso{
  \code{\link{cm.colors}},
  \code{\link{colors}}, \code{\link{palette}}, \code{\link{hsv}},
  \code{\link{rgb}}, \code{\link{gray}} and \code{\link{col2rgb}} for
  translating to RGB numbers.
}
\author{
	Wolfram Fischer
}
\examples{
twotailed.colors(12)
twotailed.colors(24,12)
showcolors( twotailed.colors(24,12) )

}
\keyword{color}
\keyword{dplot}

#---