[R] How to use curve() function without using x as the variable name inside expression?

[Philippe Grosjean]

Also note that ifelse() should be avoided as much as possible. To define a piecewise function you can use this trick:

func <- function (x, min, max) 1/(max-min) * (x >= min & x <= max)

The performances are much better. This has no impact here, but it is a good habit to take in case you manipulate such kind of functions in a more computing-intensive context (numerical integration, nls(), etc.).

funcIfElse <- function (x, min, max) ifelse(x < min | x > max, 0, 1/(max - min))
min <- 100; max <- 200; x <- 1:300
microbenchmark::microbenchmark(func(x, min, max), funcIfElse(x, min, max))
## Unit: microseconds
##                                     expr    min       lq      mean  median       uq      max neval
##             func(x, min, max) 10.242  16.0175  18.43348  18.446  19.8680   47.266   100
##  funcIfElse(x, min, max) 90.386 125.1605 148.18555 143.455 148.6695 1203.292   100

Best,

Philippe Grosjean

> On 31 Jan 2015, at 09:39, Rolf Turner <r.turner at auckland.ac.nz> wrote:
> 
> On 31/01/15 21:10, C W wrote:
>> Hi Bill,
>> 
>> One quick question.  What if I wanted to use curve() for a uniform
>> distribution?
>> 
>> Say, unif(0.5, 1.3), 0 elsewhere.
>> 
>> My R code:
>> func <- function(min, max){
>>   1 / (max - min)
>> }
>> 
>> curve(func(min = 0.5, max = 1.3), from = 0, to = 2)
>> 
>> curve() wants an expression, but I have a constant.   And I want zero
>> everywhere else.
> 
> Well if that's what you want, then say so!!!
> 
> func <- function(x,min,max) {
>   ifelse(x < min | x > max, 0, 1/(max - min))
> }
> 
> curve(func(u,0.5,1.3),0,2,xname="u")
> 
> Or, better (?) curve(func(u,0.5,1.3),0,2,xname="u",type="s")
> 
> which avoids the slight slope in the "vertical" lines.
> 
> cheers,
> 
> Rolf Turner
> 
> -- 
> Rolf Turner
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
> Home phone: +64-9-480-4619
> 
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