R help - Sep 2007 - graphs with gradients of colors

Hi All,
 
I would like to fill the area under a curve with a gradient of colors. Are there
any packages or trick I could use
 
Thanks
 
Stefan
 
 
Stefan Van Dongen
Antwerp

	[[alternative HTML version deleted]]

Maybe this information (from the R's father) can be of some help.
http://www.stat.auckland.ac.nz/~ihaka/Graphics/index.html


Van Dongen Stefan wrote:
> 
> Hi All,
>  
> I would like to fill the area under a curve with a gradient of colors. Are
> there any packages or trick I could use
>  
> Thanks
>  
> Stefan
>  
> 
-- 
View this message in context:
http://www.nabble.com/graphs-with-gradients-of-colors-tf4466780.html#a12741808
Sent from the R help mailing list archive at Nabble.com.

You could use a loop and fill small polygons with colors.

x<-seq(-3, 3, .01)
y<-eval(expression(x^3-3*x))
plot(x,y, type="n", las=1)   
n<-length(x)

# vertical bars
for(i in 1:n)
{
polygon(c(x[i], x[i], x[i+1], x[i+1]), c(min(y), y[i], y[i+1], min(y)),
border=0, col = rainbow(n)[i]) 
}

## or split each vertical bars into 100 smaller blocks
plot(x,y, type="n", las=1)
for(i in 1:n)
{
  y1<-seq(y[i], min(y), length.out=101)
  y2<-seq(y[i+1], min(y), length.out=101)
  for(j in 1:100)
  { 
    polygon(c(x[i], x[i], x[i+1], x[i+1]), c(y1[j+1], y1[j], y2[j],
y2[j+1]), border=0, col = rev(heat.colors(100))[j]) 
  }
}

Chris Stubben




Van Dongen Stefan wrote:
> 
> Hi All,
>  
> I would like to fill the area under a curve with a gradient of colors. Are
> there any packages or trick I could use
>  
> Thanks
>  
> Stefan
>  
>  
> Stefan Van Dongen
> Antwerp
> 
> 
> 
> 
-- 
View this message in context:
http://www.nabble.com/graphs-with-gradients-of-colors-tf4466780.html#a12743725
Sent from the R help mailing list archive at Nabble.com.

Van Dongen Stefan wrote:
> Hi All,
>  
> I would like to fill the area under a curve with a gradient of colors. Are
there any packages or trick I could use
>  
> 
Hi Stefan,

Chris has answered the question of how to define the polygons, so I'll 
have a shot at the gradient. The plotrix package has three functions 
that produce color gradients, smoothColors, color.gradient and color.scale.

smoothColors allows you to specify the extreme, and optionally 
intervening, colors and interpolates colors between the ones you have 
specified.

color.gradient is quite similar, except that the user can specify the 
red, green and blue components separately.

color.scale turns numeric values into colors using the same method of 
color specification as color.gradient. It will also work with just the 
extreme colors.

The RColorBrewer package also has the capability to produce color 
gradients. There may be other packages that will do what you want as well.

Jim

The first question you should ask is "why do you want to do this?".
Adding gradients and other things like that can make a graph look neat,
but can also distort the information in the graph.  You should carefully
consider whether doing things like this really help the graph, or
distract from it.

If you do create a graph with the gradient, you should also create one
without the gradient and compare them to see which conveys the important
information better.

If you decide to go ahead with this, there was a discussion a while ago
on including pictures as the background of bar charts, you could use
something similar to that but with a gradient instead of a picture.  For
some cases it may be easier to create your graph, then use another tool
like imagemagick or gimp to replace a color with the gradient.

If you want to do it in R, then here are a couple of options to get you
started (your specifics will vary depending on the curve you want to
use, how smooth you want things to look, etc.

xx <- seq( -3,3, length=250 )
yy <- dnorm(xx, 0, 1)

plot(xx,yy, type='l')
tmp <- par('usr')

par(new=TRUE)

image( tmp[1:2], seq( tmp[3], tmp[4], len=101 ), 
  matrix( 1:100, ncol=100, nrow=1), add=TRUE,
  col=heat.colors(100))

polygon( c(tmp[1],xx,tmp[2],tmp[2],tmp[1] ), 
  c(yy[1], yy, yy[ length(yy) ], tmp[4], tmp[4] ), 
  col='white', border='white')
polygon( c(tmp[1], tmp[2], tmp[2], tmp[1] ),
  c(yy[1],yy[1], tmp[3], tmp[3]), col='white', border='white')

lines(xx,yy)
box()

# this one may be a bit of overkill for most cases, but does give more
# flexibility

library(TeachingDemos)

xx <- seq(0, 2*pi, length=100)
yy <- sin(xx)

plot(xx,yy, type='l', ylim=c(-1.1, 1.1))

tmpfun <- function(...){
   image( c(0,2*pi), seq(-1.1,1.1,length=101), matrix( 1:100, nrow=1 ),
	col=terrain.colors(100), add=TRUE )
}

xxx <- embed(xx,2)
for( i in 1:99 ){
	clipplot( tmpfun(), c(xxx[i,2],xxx[i,1]), c(-1.1,
(yy[i]+yy[i+1])/2 ) )
}

lines(xx,yy)

# shade from 0

plot(xx,yy, type='l', ylim=c(-1.1, 1.1))

tmpfun <- function(...){
   image( c(0,2*pi), seq(-1.1,1.1,length=101), matrix( 1:100, nrow=1 ),
	col=terrain.colors(100), add=TRUE )
}

xxx <- embed(xx,2)
for( i in 1:99 ){
	clipplot( tmpfun(), c(xxx[i,2],xxx[i,1]), c(0, (yy[i]+yy[i+1])/2
) )
}

lines(xx,yy)


Use at your own risk and definitly compare them to simple plots for
clarity.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 
 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Van Dongen Stefan
> Sent: Monday, September 17, 2007 7:37 AM
> To: R-help at stat.math.ethz.ch
> Subject: [R] graphs with gradients of colors
> 
> Hi All,
>  
> I would like to fill the area under a curve with a gradient 
> of colors. Are there any packages or trick I could use
>  
> Thanks
>  
> Stefan
>  
>  
> Stefan Van Dongen
> Antwerp
> 
> 	[[alternative HTML version deleted]]
> 
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