Percentage of a maximum value within a group

[Sam Albers]

Hello there,

I am sort of running in circle with a trouble as I know there is a better way than my current moethod but can't seem to figure it out. I'd like to figure out the "percentage of a maximum value within a group". Using the iris dataset here is what I am currently doing:

library(plyr)

iris1<-merge(
  ddply(iris, .(Species), summarize,
      maxPetal.Width=max(Petal.Width)
      ),
  iris, by=c("Species")
)

iris1$PerMax<-round(iris1$Petal.Width/iris1$maxPetal.Width, 2)
iris1

However, this seems cumbersome and I feel like there is a way to do this all while one instance of ddply. Can anyone recommend a better way of getting at this?

Thanks in advance!

Sam

[Hadley Wickham]

Hint: try mutate instead of summarise.
Hadley

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[Sam Albers]

A fairly comprehensive hint.

Using mutate:

ddply(iris, .(Species), mutate,
      per = round(Petal.Width/max(Petal.Width),2)
)

Thanks Hadley!!!

Sam