R help - May 2012 - Identifying case by groups in a data frame

Hi everyone,

I would like to identify the case by groups that is just bigger that 
avg plus sd. For example, using species as group and petal.wid as my 
variable in the iris data.
What's the better way to doit? creating a function?

So,the question is to identify the single element of each species that is just
larger than a cut-off point (i.e. larger than mean + sd)
I made this, but I can not make a relation to to orginal data for identifiying
the cases.If you have some lights please share it.

data(iris)

library(plyr)
petal.wid.avg <-ddply(iris,.(Species),function(df)
  return(c(petal.wid.avg=mean(df$Petal.Width),petal.wid.sd=sd(df$Petal.Width)))
)
petal.wid.avg$avgsd <-petal.wid.avg$petal.wid.avg +petal.wid.avg$petal.wid.sd
petal.wid.avg


Thanks in advance:
José
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Dear José,

Here is one way:

# aux. function
foo <- function(x, ...){
            m <- mean(x, ...)
            S <- sd(x, ...)
            x > m + S
            }

# result
iris$rule <- with(iris, ave(Petal.Width, list(Species), FUN = foo))
head(iris)

HTH,
Jorge.-


On Thu, May 3, 2012 at 5:19 PM, Jose Bustos Melo <> wrote:
> Hi everyone,
>
> I would like to identify the case by groups that is just bigger that
> avg plus sd. For example, using species as group and petal.wid as my
> variable in the iris data.
> What's the better way to doit? creating a function?
>
> So,the question is to identify the single element of each species that is
> just larger than a cut-off point (i.e. larger than mean + sd)
> I made this, but I can not make a relation to to orginal data for
> identifiying the cases.If you have some lights please share it.
>
> data(iris)
>
> library(plyr)
> petal.wid.avg <-ddply(iris,.(Species),function(df)
>   return(c(petal.wid.avg=mean(df$Petal.Width),petal.wid.sd
> =sd(df$Petal.Width)))
> )
> petal.wid.avg$avgsd <-petal.wid.avg$petal.wid.avg +petal.wid.avg$
> petal.wid.sd
> petal.wid.avg
>
>
> Thanks in advance:
> José
>        [[alternative HTML version deleted]]
>
>
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>
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