R help - Mar 2006 - Plotting a segmented function

This might be a trivial question, but I would appreciate if anybody
could suggest an elegant way of plotting a function such as the
following (a simple distribution function):
F(x) = 0 if x<=0
       =(x^2)/2 if 0<x<=1
       =2x-((x^2)/2)-1 if 1<x<=2
       =1 if x>2
This is just an example. In this case it is a continuous function. But
how to do it in general in an elegant way.
I've done the following:
x1 <- seq(-1,0,.01)
f1 <- rep(0,101)
x2 <- seq(0,1,.01)
f2 <- 0.5*(x2^2)
x3 <- seq(1,2,.01)
f3 <- (2*x3)-(0.5*(x3^2))-1
x4 <- seq(2,3,.01)
f4 <- rep(1,101)
x <- c(x1,x2,x3,x4)
F <- c(f1,f2,f3,f4)
plot(x,F,type='l')

But this seems very cumbersome.
Any help is much appreciated.

Thanks
Jacob


Jacob L van Wyk
Department of Statistics
University of Johannesburg APK
P O Box 524
Auckland Park 2006
South Africa
Tel: +27-11-489-3080
Fax: +27-11-489-2832

Jacob van Wyk wrote:
> This might be a trivial question, but I would appreciate if anybody
> could suggest an elegant way of plotting a function such as the
> following (a simple distribution function):
> F(x) = 0 if x<=0
>        =(x^2)/2 if 0<x<=1
>        =2x-((x^2)/2)-1 if 1<x<=2
>        =1 if x>2
> This is just an example. In this case it is a continuous function. But
> how to do it in general in an elegant way.
> I've done the following:
> x1 <- seq(-1,0,.01)
> f1 <- rep(0,101)
> x2 <- seq(0,1,.01)
> f2 <- 0.5*(x2^2)
> x3 <- seq(1,2,.01)
> f3 <- (2*x3)-(0.5*(x3^2))-1
> x4 <- seq(2,3,.01)
> f4 <- rep(1,101)
> x <- c(x1,x2,x3,x4)
> F <- c(f1,f2,f3,f4)
> plot(x,F,type='l')
> 
> But this seems very cumbersome.
> Any help is much appreciated.

Define a function such as

f <- function(x){

     (x>2) +
     (2*x-((x^2)/2)-1) * ((1 < x) & (x <= 2)) +
     ((x^2)/2) *  ((0 < x) & (x <= 1))
}

curve(f, from = -1, to = 3)

> Thanks
> Jacob
> 
> 
> Jacob L van Wyk
> Department of Statistics
> University of Johannesburg APK
> P O Box 524
> Auckland Park 2006
> South Africa
> Tel: +27-11-489-3080
> Fax: +27-11-489-2832
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

You could try nested ifelse statements,

something like (untested)

x <- seq(-1, 3, 0.1)
 y <- ifelse( x <= 3,
	    ifelse( x <= 2,
		ifelse( x <= 1,
		    ifelse( x <= 0, 0, x^2/2), 2 * x - (x^2/2) -1),  1) )
plot(x, y)

**************************************
This might be a trivial question, but I would appreciate if anybody
could suggest an elegant way of plotting a function such as the
following (a simple distribution function):
F(x) = 0 if x<=0
       =(x^2)/2 if 0<x<=1
       =2x-((x^2)/2)-1 if 1<x<=2
       =1 if x>2
This is just an example. In this case it is a continuous function. But
how to do it in general in an elegant way.
I've done the following:
x1 <- seq(-1,0,.01)
f1 <- rep(0,101)
x2 <- seq(0,1,.01)
f2 <- 0.5*(x2^2)
x3 <- seq(1,2,.01)
f3 <- (2*x3)-(0.5*(x3^2))-1
x4 <- seq(2,3,.01)
f4 <- rep(1,101)
x <- c(x1,x2,x3,x4)
F <- c(f1,f2,f3,f4)
plot(x,F,type='l')

But this seems very cumbersome.
Any help is much appreciated.

Thanks
Jacob


-- 
Ken Knoblauch
Inserm U371
Cerveau et Vision
Dept. of Cognitive Neuroscience
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69500 Bron
France
tel: +33 (0)4 72 91 34 77
fax: +33 (0)4 72 91 34 61
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http://www.lyon.inserm.fr/371/