R help - Jul 2003 - curves with shaded areas?

Hi,

I want to make a plot with abline where the area below or above the 
curve is shaded. I can't find any documentation on that. Can anybody 
help me with that?

thanks, Juffi

See ?polygon, ?rect for how to shade areas.

If you make a plot with abline, surely it has no curves (only straight 
lines)?

On Tue, 22 Jul 2003, Johannes Fuernkranz wrote:
> I want to make a plot with abline where the area below or above the 
> curve is shaded. I can't find any documentation on that. Can anybody 
> help me with that?
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

polygon() together with par("usr") would be your friend here. As I do
not know if you want horisontal/vertical lines or any line, here is a
general example:

# Generate the data
x <- seq(from=1, to=3.5*pi, length=100)
y <- sin(x)

# Creates an empty plot of right size
plot(x,y, type="n")  

# Get plotting region
x0 <- par("usr")[1]; x1 <- par("usr")[2];
y0 <- par("usr")[3]; y1 <- par("usr")[4];

last <- length(y)

# Create the "upper" polygon
polygon(c(x0,x0,x,x1,x1), c(y1,y[1],y,y[last],y1), col="#ffcccc",
border=NA)
# Create the "lower" polygon
polygon(c(x0,x0,x,x1,x1), c(y0,y[1],y,y[last],y0), col="#ccccff",
border=NA)

# Plot the data on top
points(x,y)

As you see, as there are 4% margins by default, you have to specify what
you want to do at the margins. Depending on if you want regions defined
by abline(h)/abline(v) or by abline(a,b) you solution will be somewhat
different. 

Cheers

Henrik Bengtsson
Lund University
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> Johannes Fuernkranz
> Sent: den 22 juli 2003 12:10
> To: r-help at stat.math.ethz.ch
> Subject: [R] curves with shaded areas?
> 
> 
> Hi,
> 
> I want to make a plot with abline where the area below or above the 
> curve is shaded. I can't find any documentation on that. Can anybody 
> help me with that?
> 
> thanks, Juffi
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list 
> https://www.stat.math.ethz.ch/mailman/listinfo> /r-help
> 
> 
>

> De : r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch]De la part de Johannes
> Fuernkranz
[...]
> I want to make a plot with abline where the area below or above the
> curve is shaded. I can't find any documentation on that. Can anybody
> help me with that?
[...]

You have to play with par("usr").

See the toy example below, perhaps a little naive, but it seems to do what
you want.

##
tmp<-rnorm(100)
mydf<-data.frame(x=tmp, y=0.5*tmp+rnorm(100))
plot(y~x, mydf)
myreg<-lm(y~x, mydf)
abline(myreg)
x1<-par("usr")[1:2]
y1<-par("usr")[3]
myxy<-rbind(
  cbind(x1, predict(myreg, data.frame(x=x1))),
  cbind(rev(x1), rep(y1,2))
)
polygon(myxy, col="grey")
##

I hope it helps.

Christophe
--
Christophe DECLERCQ, MD
Observatoire R?gional de la Sant? Nord-Pas-de-Calais
13, rue Faidherbe 59046 LILLE Cedex FRANCE
Phone +33 3 20 15 49 24
Fax   +33 3 20 55 92 30
E-mail c.declercq at orsnpdc.org