R help - Oct 2007 - How to modify function for list

Dear R Gurus,

I have a function which calculate the BMI standard deviation score
based on the age and gender specific L, M, S value.
I have written a function like this

bmisds <- function (age, gender, bmi){
  if (age ==1 & gender ==1)
    {
      bmif <- c(-1.013,16.133,0.07656)
    }
  else if (age ==1 & gender ==0)
    {
      bmif <- c(-1.79,16.421,0.07149)
    }
  else if (age == 2 & gender == 1)
    {
      bmif <- c(-1.403,15.58,0.07342)
    }
  else if (age == 2 & gender == 0)
    {
      bmif <- c(-2.045,15.861,0.07116)
    }
....

      (((bmi/bmif[2])**bmif[1] -1)/(bmif[1]*bmif[3]))
}

This function work when I supply a single variable, e.g. bmisds(1,0,16)

When I try it with a list, e.g.
age <- c(12,13,14)
gender <- c(0,1,1)
bmi <- c(14,15,16)
bmisds(age,gender,bmi)

This function give me wrong answer and error msg.
Warning messages:
1: the condition has length > 1 and only the first element will be
used in: if (age == 1 & gender == 1) {


How can I midify this function to work with list/vector?

regards,
C


-- 
CH Chan
Research Assistant - KWH
http://www.macgrass.com

Instead of 
> bmisds(age,gender,bmi)
Try the vectorized version 
> mapply(bmisds, age, gender, bmi)
See ?mapply

-Christos

 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Chung-hong Chan
> Sent: Wednesday, October 03, 2007 12:31 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] How to modify function for list
> 
> Dear R Gurus,
> 
> I have a function which calculate the BMI standard deviation 
> score based on the age and gender specific L, M, S value.
> I have written a function like this
> 
> bmisds <- function (age, gender, bmi){
>   if (age ==1 & gender ==1)
>     {
>       bmif <- c(-1.013,16.133,0.07656)
>     }
>   else if (age ==1 & gender ==0)
>     {
>       bmif <- c(-1.79,16.421,0.07149)
>     }
>   else if (age == 2 & gender == 1)
>     {
>       bmif <- c(-1.403,15.58,0.07342)
>     }
>   else if (age == 2 & gender == 0)
>     {
>       bmif <- c(-2.045,15.861,0.07116)
>     }
> ....
> 
>       (((bmi/bmif[2])**bmif[1] -1)/(bmif[1]*bmif[3])) }
> 
> This function work when I supply a single variable, e.g. 
> bmisds(1,0,16)
> 
> When I try it with a list, e.g.
> age <- c(12,13,14)
> gender <- c(0,1,1)
> bmi <- c(14,15,16)
> bmisds(age,gender,bmi)
> 
> This function give me wrong answer and error msg.
> Warning messages:
> 1: the condition has length > 1 and only the first element 
> will be used in: if (age == 1 & gender == 1) {
> 
> 
> How can I midify this function to work with list/vector?
> 
> regards,
> C
> 
> 
> --
> CH Chan
> Research Assistant - KWH
> http://www.macgrass.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.
> 
>

Yes, I tried. Wrong calculation.


On 10/3/07, Stefan Grosse <singularitaet at gmx.net>
wrote:
> On Wednesday 03 October 2007 08:23:15 Chung-hong Chan wrote:
> CC >
> CC > Suppose I have a long list of age, gender and bmi from a data.frame
> CC > called msltdata.
> CC >
> CC > > age <- msltdata$age
> CC > > gender <- msltdata$data
> CC > > bmi <-msltdata$bmi
> CC > > age
> CC > [1]  5 10 14
> CC > > gender
> CC > [1] 0 0 0
> CC > Levels: 0 1
> CC > > bmi
> CC > [1] 17.17693 16.40702 16.87695
> CC > > mapply(bmisds,age,gender,bmi)
>
> have you tried
> bmisds(msltdata$age,msltdata$data,msltdata$bmi)
> ?
>

-- 
CH Chan
Research Assistant - KWH
http://www.macgrass.com