[R] Weighted mad

[ONKELINX, Thierry]

You could try something like this.

library(plyr)
ddply(pool, .(ym), function(z){
	weighted.mean(x= z$SMM, w = z$wght)
})

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx op inbo.be
www.inbo.be

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~ Sir Ronald Aylmer Fisher

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-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org] Namens Bond, Stephen
Verzonden: dinsdag 7 februari 2012 15:55
Aan: r-help op r-project.org
Onderwerp: [R] Weighted mad

Greetings UseRs,

Pls advise if there is a way to write a func that can be supplied to aggregate to compute weighted MeanAbsolute Dev (MAD). I am having trouble passing the correct weights from each group level and cannot see the code behind aggregate. But maybe 'aggregate' is not the best way to do that.

> m1 <- aggregate(pool[,c("SMM")],by=list(time=pool$ym),weighted.mean,w=pool$wght)
Error in weighted.mean.default(X[[1L]], ...) : 
  'x' and 'w' must have the same length

Apparently the grouping does not work on the additional argument. I am using weighted mean here just to be explicit and avoid supplying a custom function gor weighted MAD, which is not difficult to write by itself. It's making it work with aggreagte that is the problem. 

> aggregate
function (x, ...) 
UseMethod("aggregate")
<environment: namespace:stats>

Does not show anything...

Stephen B

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