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Rolf Turner

2015-Jan-31 08:39 UTC

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

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

peter dalgaard

2015-Jan-31 08:58 UTC

head link

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

> 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))
> }
> 
Oy! help(Uniform) called. I wants its density function back...
> 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.
It might put the verticals in the wrong place though. I usually just increase
the "n" parameter:

curve(dunif(u,.5, 1.3), from=0, to=2, n=5001, xname="u") 


-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

Philippe Grosjean

2015-Jan-31 09:03 UTC

head link

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

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
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Ben Tupper

2015-Jan-31 14:39 UTC

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

Hi Philippe,

Ah!  Thanks for pointing out the pesky ifelse() issue.  I have only recently
been learning (the hard way) that ifelse() is not a tool for the uninformed like
me, but it is ever so tempting!

I would like to offer another way to speed things up. findInterval() can be
quite fast, and the speed up is most noticeable when the size of the input grows
(note I made input x <- 1:3000).

func <- function (x, mn, mx) 1/(mx-mn) * (x >= mn & x <= mx)

funcIfElse <- function (x, mn, mx) ifelse(x < mn | x > mx, 0, 1/(mx -
mn))

funcFindInterval <- function(x, mn, mx)  1/(mx - mn) * (findInterval(x, c(mn,
mx), rightmost.closed = TRUE) == 1)
        
mn<- 100; mx <- 200; x <- 1:3000
microbenchmark::microbenchmark(func(x, mn, mx), funcIfElse(x, mn, mx),
funcFindInterval(x, mn, mx))

#Unit: microseconds
#                        expr     min      lq      mean   median       uq     
max neval
#             func(x, mn, mx)  74.920  76.006  88.57119  76.5635  78.7065 
897.333   100
#       funcIfElse(x, mn, mx) 728.388 733.206 832.02225 735.4280 796.1910
1645.804   100
# funcFindInterval(x, mn, mx)  33.954  35.334  56.57323  36.5010  38.3340 
993.193   100

r1 <- func(x, mn, mx)
r2 <- funcIfElse(x, mn, mx)
r3 <- funcFindInterval(x, mn, mx)

identical(r1, r2)
#[1] TRUE
identical(r2, r3)
#[1] TRUE

Cheers,
Ben


On Jan 31, 2015, at 4:03 AM, Philippe Grosjean <phgrosjean at
sciviews.org> wrote:
> 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
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

R help - Jan 2015 - How to use curve() function without using x as the variable name inside expression?

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

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

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

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