Dear Stephen
The names of methods of aggregate can be viewed with the methods argument.
Typing aggregate.data.frame shows you the method used for data frames.
> methods(aggregate)
[1] aggregate.data.frame aggregate.default aggregate.formula*
[4] aggregate.ts
Non-visible functions are asterisked
However, you need the function by, which passes a data frame to the function.
> pool <- data.frame(SMM = rnorm(10), ym = rep(1:2, each = 5), wght = 1)
> pool
SMM ym wght
1 0.904640493 1 1
2 1.021857174 1 1
3 1.234153020 1 1
4 -0.697625918 1 1
5 0.073146470 1 1
6 1.438553786 2 1
7 -0.831183333 2 1
8 -0.055872825 2 1
9 0.858622161 2 1
10 0.001968816 2 1
> mad <- by(pool, pool$ym,
+ function(pool) { weighted.mean(x = pool$SMM, w = pool$wght) })
> mad[1:2]
pool$ym
1 2
0.5072342 0.2824177
Regards,
Chris Campbell
MANGO SOLUTIONS
Data Analysis that Delivers
+44 1249 767700
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Bond, Stephen
Sent: 07 February 2012 14:55
To: r-help@r-project.org
Subject: [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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Kind Regards
Chris Campbell
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