R help - Jul 2011 - Plotting a function that includes logical operators

I am trying to plot the following function over the range 0-100

test <- function(t){{
if (t<=10)
x<-t*0
else x<-2*t
}
x
}

when I use plot(test,0,100) the GUI produces the following;

"Warning message:
In if (t <= 10) x <- t * 0 else x <- 2 * t :
  the condition has length > 1 and only the first element will be used"

I am confused as when I evaluate the function for individual t it gives the
correct response i.e. 0 for t<=10 and 2*t for t>10... This is what I wish
the function to do however, I am not able to plot the function.

Any help would be most appreciated!


--
View this message in context:
http://r.789695.n4.nabble.com/Plotting-a-function-that-includes-logical-operators-tp3697732p3697732.html
Sent from the R help mailing list archive at Nabble.com.

On Jul 27, 2011, at 3:01 AM, dean123 wrote:
> I am trying to plot the following function over the range 0-100
>
> test <- function(t){{
> if (t<=10)
> x<-t*0
> else x<-2*t
> }
> x
> }
>
Two problems I see. The first is the one described fairly clearly by  
the error message:

Read:

?"if"

It is not designed to handle vectors.

You most certainly should read:

?ifelse

> when I use plot(test,0,100) the GUI produces the following;
>
The second is that you have created a function to which you have  
offered no arguments. Typing plot(test, 0, 100) is not passing any  
arguments to 'test'. It is giving test, 0, and 100 to 'plot' and
since
they are unnamed you are futher expecting R to associate test with x,  
0 with y and 100 with whatever the third argument plot might be. (You  
should look it up.)

?plot

You need to learn to form you commands as  
function_name(arg_name=arg_value, ...) and realize that function calls  
can also be arguments so once you have a working 'test' it might be  
successful to use this

plot( seq(100), test(seq(100) )

See read more of Introduction to R and work all the examples.

-- 
David.
> "Warning message:
> In if (t <= 10) x <- t * 0 else x <- 2 * t :
>  the condition has length > 1 and only the first element will be
used"
>
> I am confused as when I evaluate the function for individual t it  
> gives the
> correct response i.e. 0 for t<=10 and 2*t for t>10... This is what I
> wish
> the function to do however, I am not able to plot the function.
>
> Any help would be most appreciated!
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Plotting-a-function-that-includes-logical-operators-tp3697732p3697732.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
David Winsemius, MD
West Hartford, CT

Hi David,

I am trying to define t as a single numeric value and not as a vector.. I
want the function to realise that if I call test(t) and t is less than equal
10 return zero, if t greater than 10 return 2*t. Am i missing some code in
which to define t a numeric value instead of a vector?

Also, I thought that by defining test <- function(t) {...} I was defining t
as the argument of the function?

Thanks,
Dean

--
View this message in context:
http://r.789695.n4.nabble.com/Plotting-a-function-that-includes-logical-operators-tp3697732p3698464.html
Sent from the R help mailing list archive at Nabble.com.