[R] max value

[Petr PIKAL]

Hi

> 
> On 2012-05-15 08:36, Melissa Rosenkranz wrote:
> > Here is an R problem I am struggling with:
> > My dataset is organized like this...
> >
> > subject       session        variable_x       variable_y
> > 01                 1                    1<interger values>
> > 01                 1                    2
> > 01                 1                    3
> > 01                 2                    1
> > 01                 2                    2
> > 01                 2                    3
> > 02                 1                    1
> > 02                 1                    2
> > 02                 1                    3
> > 02                 2                    1
> > 02                 2                    2
> > 02                 2                    3
> > 03                 1                    1
> > 03                 1                    2
> > 03                 1                    3
> > 03                 2                    1
> > 03                 2                    2
> > 03                 2                    3
> > ...
> >
> > I need to find the level of variable x at which variable y has the 
maximum
> > value for each individual for each session. Then, I need to create 
another
> > variable, say variable "z" that labels that row in the dataset as the 
"max"
> > for that individual at that time. I have searched the archives and the 
web
> > for ideas, but am having trouble finding appropriate search terms for 
what
> > I need to do. Any advice? Thank you!!
> >
> 
> This is one way:

Here is another

d$z<-ave(d$y, d$subject, d$session, FUN=function(x) x==max(x))

Regards
Petr

> 
>    set.seed(123)
>    d <- data.frame(
>         subject = gl(3,6,labels=c("01","02","03")),
>         session = gl(2,3,18),
>         x = gl(3,1,18),
>         y = sample(11:15, 18, replace=TRUE))
> 
>    library(plyr)
>    ddply(d, .(subject, session), transform,
>          z = ifelse(y == max(y), 1, 0))
> 
> Peter Ehlers
> 
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