R help - Aug 2010 - The condition has length > 1 and only the first element will be used

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

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
  }
}
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)

best regards,

-- 
Pablo de Camargo Cerdeira
pablo at fgv.br
pablo.cerdeira at gmail.com
+55 (21) 3799-6065

Hi

r-help-bounces at r-project.org napsal dne 03.08.2010 13:03:33:
> 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
> 
> 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?
Your function takes only one scalar argument so you can not use it on 
vector.

Hint. Look at See also help page of if command.

Regards
Petr
> 
> mod = function(x) {
>   if (x < 0) {
>     mod <- x*(-1)
>   }
>   else {
>     mod <- x
>   }
> }
> 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)
> 
> best regards,
> 
> -- 
> Pablo de Camargo Cerdeira
> pablo at fgv.br
> pablo.cerdeira at gmail.com
> +55 (21) 3799-6065
> 
> ______________________________________________
> 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.

Look at the help page for 'if':

"A length-one logical vector that is not NA. Conditions of length
greater than one are accepted with a warning, but only the first
element is used. Other types are coerced to logical if possible,
ignoring any class."

If you want the positive value, why aren't you using 'abs'?

You might want to look at the 'ifelse' function to work with vectors.
You would do something like:

mod <- ifelse(x < 0, x * (-1), x)

You probably need to re-read the Intro to R to understand more about
vectorized operators/operations.

On Tue, Aug 3, 2010 at 7:03 AM, Pablo Cerdeira <pablo.cerdeira at
gmail.com> 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
>
> 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
> ?}
> }
> 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)
>
> best regards,
>
> --
> Pablo de Camargo Cerdeira
> pablo at fgv.br
> pablo.cerdeira at gmail.com
> +55 (21) 3799-6065
>
> ______________________________________________
> 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

Ok thanks, but I have found the solution: "ifelse".

Here goes a working version of the code:

mod = function(x) {
  ifelse(x < 0,x*(-1),x)
}
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)

best regards


On Tue, Aug 3, 2010 at 8:03 AM, Pablo Cerdeira <pablo.cerdeira at
gmail.com> 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
>
> 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
> ?}
> }
> 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)
>
> best regards,
>
> --
> Pablo de Camargo Cerdeira
> pablo at fgv.br
> pablo.cerdeira at gmail.com
> +55 (21) 3799-6065
>


-- 
Pablo de Camargo Cerdeira
pablo at fgv.br
pablo.cerdeira at gmail.com
+55 (21) 3799-6065

Hello, Pablo,

if() doesn't accept a vector as its argument the way you may want it to; 
take a look at ifelse().

  Regards  --  Gerrit


On Tue, 3 Aug 2010, 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
>
> 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
>  }
> }
> 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)
>
> best regards,
>
> -- 
> Pablo de Camargo Cerdeira
> pablo at fgv.br
> pablo.cerdeira at gmail.com
> +55 (21) 3799-6065
>
> ______________________________________________
> 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.
>
---------------------------------------------------------------------
AOR Dr. Gerrit Eichner               Mathematical Institute, Room 212
gerrit.eichner at math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
Fax: +49-(0)641-99-32109              http://www.uni-giessen.de/~gcb7

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