# [R] How to modify function for list

Chung-hong Chan chainsawtiney at gmail.com
Wed Oct 3 08:23:15 CEST 2007

```Thanks for your answer. But I have a strange question that I don't
know how to explain and I really don't know how to spot the
problematic part.

Suppose I have a long list of age, gender and bmi from a data.frame
called msltdata.

> age <- msltdata\$age
> gender <- msltdata\$data
> bmi <-msltdata\$bmi
> age
[1]  5 10 14
> gender
[1] 0 0 0
Levels: 0 1
> bmi
[1] 17.17693 16.40702 16.87695
> mapply(bmisds,age,gender,bmi)

however, when I try to create the vectors once again using the same data, i.e.
> age <- c(5,10,14)
> gender <- c(0,0,0)
> bmi <- c(17.17693,16.40702,16.87695)
> mapply(bmisds,age,gender,bmi)

This time, I can get the correct calculation.
Would anyone please give me some hints to find out what's went wrong?

Regards,
C

On 10/3/07, Christos Hatzis <christos at nuverabio.com> wrote:
>
> > 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
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> >
>
>
>

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

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