new standardised variable based on group membership

That works a treat Thierry, thanks! I wasn't aware of the plyr package but I like what it does- I'll put it to use work in the future.

Regards

John

-----Original Message-----
From: ONKELINX, Thierry [mailto:Thierry.ONKELINX at inbo.be]
Sent: Monday, 3 October 2011 6:36 PM
To: Morrongiello, John (CMAR, Hobart); r-help at r-project.org
Subject: RE: [R] new standardised variable based on group membership

Dear John,

You need to combine scale with a grouping function.

data(Orange)
library(plyr)
Orange <- ddply(Orange, .(Tree), function(x){
? ? ? ?x$ddplyAge <- scale(x$age)[, 1]
? ? ? ?x
})

Orange$aveAge <- ave(Orange$age, by = Orange$Tree, FUN = scale)

all.equal(Orange$ddplyAge, Orange$aveAge)

Best regards,

Thierry

-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens John.Morrongiello at csiro.au
Verzonden: maandag 3 oktober 2011 7:34
Aan: r-help at r-project.org
Onderwerp: [R] new standardised variable based on group membership

Hi
I have a data comprised of repeated measures of growth (5-15 records per
individual) for 580 fish (similar to Orange dataset from nlme library). I would like
to standardise these growth measures (yi ? ?/sd) using mean and standard
deviation unique to each fish. Can someone suggest a function that would help
me do this? I?ve had a look at scale and sweep but can?t find a worked example
that does what I?m after

Cheers

John


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