[R] The condition has length > 1 and only the first element will be used

[David Winsemius]

On Aug 3, 2010, at 7:03 AM, Pablo Cerdeira wrote:

> Hi All,
>
> I'm trying to run the following script in R, but I'm getting a  
> warning saying:
>
> Warning message:
> In if (z < 0) { :
>  the condition has length > 1 and only the first element will be used

ifelse is the proper function rather than if{}else{}. Read:

?ifelse
?Control


>
> As you can see, I'm sending a vector x to the function f without any
> problem. The function f calculates the y value for each x.
>
> But the function f needs to convert the x to positive values (the mod
> function). And when it tries to convert, it always uses the first
> value of x.
>
> What I'm doing wrong here?
>
> mod = function(x) {
>  if (x < 0) {
>    mod <- x*(-1)
>  }
>  else {
>    mod <- x
>  }
> }

Try instead one of:

mod <- function (x) (x < 0)*(-1)*x + (x >= 0)*x

mod <- function (x) ifelse( x < 0 ,  -x, x)

mod <- abs


> f = function(x) {
>  f <- mod(x)/x
> }
> x <- seq(-1,1,0.01)
> x
> y <- f(x)
> y
> plot(f,xlim = c(-1,1))
> remove(x,y,f,mod)

You didn't provide any data, nor did you indicate problems with that  
code, so I am not commenting on that.

David Winsemius, MD
West Hartford, CT