R help - Apr 2002 - zero center a group of variables

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A simple question, perhaps to simple, but I am new to R:
For a data frame with k variables and n1+n2 observations (two 
groups) how can i substract the group means for every variable, so 
both group variables become centered to mean zero?

Thanks in advance for your help

H?ctor



...................................................
H?ctor Villalobos
  Depto. de Pesquer?as y Biolog?a Marina
  Instituto Polit?cnico Nacional - Centro
  Interdisciplinario de Ciencias Marinas 
  (IPN-CICIMAR)
  A.P. 592. Col. Centro
  La Paz, Baja California Sur, M?XICO. 23000
  Tel.: (+52 612) 122 53 44 ext. 2426 
  Fax.: (+52 612) 122 53 22
....................................................

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"H?ctor Villalobos" <hvillalo at ipn.mx> writes:
> A simple question, perhaps to simple, but I am new to R:
> For a data frame with k variables and n1+n2 observations (two 
> groups) how can i substract the group means for every variable, so 
> both group variables become centered to mean zero?
> 
> Thanks in advance for your help
> 
> H?ctor
in 1.5.0, we'll have

 split(x, g) <- lapply(split(x, g), scale, scale=FALSE)

Till then, you'll have to do something like

x[g==1,] <- scale(x[g==1,], scale=FALSE)
x[g==2,] <- scale(x[g==2,], scale=FALSE)

or, more general

for ( i in split(1:length(g), g) )
   x[i,] <- scale(x[i,], scale=FALSE)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
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