[R] group mean, minus each row's value

Dimitris Rizopoulos dimitris.rizopoulos at med.kuleuven.be
Tue Nov 13 17:07:32 CET 2007

do you mean something like this:

tapply(x, g, function (y) {
    sapply(1:length(y), function (i) mean(y[-i]))

I hope it helps.


Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/

----- Original Message ----- 
From: "Casey Klofstad" <klofstad at gmail.com>
To: <r-help at r-project.org>
Sent: Tuesday, November 13, 2007 4:45 PM
Subject: [R] group mean, minus each row's value

>I used the following to assign each row the group average, where w is
> the new group average variable, x is the variabale to be averaged, 
> and
> g is the nominal group indicator:
> w <- ave(x,g)
> Now I want to calculate the group average, but WITHOUT each row's
> value of x. Is there an easy way to do this? I'm sure I'm missing
> something obvious here, but for the life of me I can't figure it 
> out.
> Thanks!
> -- 
> Casey A. Klofstad
> University of Miami
> Department of Political Science
> Coral Gables, FL
> klofstad at gmail.com
> http://moya.bus.miami.edu/~cklofstad
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