[R] Simple question regarding domain restrictions/piecewise functions in R

chad.mills chad.mills at gmail.com
Mon Mar 26 00:08:56 CEST 2012

I am a novice R user.

I would like to be able to graph some simple piecewise functions/functions
with domain restrictions in R, but I'm having trouble defining such
functions.  For example, I would like to define the following function:

f(x)={x^2 if -1<x<x; 1 if 2<x<3}

Notably, the function is undefined outside of domain (-1,1)U(2,3).  My best
attempt in R is something like this:

f<-function(x) ifelse(-1<x & x<1,x^2,ifelse(2<=x & x<=3,1,as.null())) 

This approach works fine for values within the domain.  But, naturally, when
I try values outside of the domain I get an error.  Consequently, when I try
to graph such a function:


I get the following error: 

Error in ifelse(2 <= x & x <= 3, 1, as.null()) : 
  replacement has length zero

I realize that I could create vectors of x-y points and plot using the
plot(x,y) command, but it seems to me that I should be able to define a
piecewise function symbolically and just graph it.  Am I wrong?  Any help
would be greatly appreciated.

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