Thanks! :-)
I suppose it's obvious, but one will generally have to use a (anonymous)
function to 'unpack' the data.frame into columns, unless the function
already knows how to do this.
I mention this because when I tested the solution on my example I got an
unexpected result -- apparently weighted.mean will operate on a 2-column
dataframe but not in the way one would expect.
data = 1:10
weights = rep(1,10)
groups = rep(c(1,2),5)
by( data.frame(data,weights), groups, weighted.mean)
groups: 1
[1] 15
------------------------------------------------------------
groups: 2
[1] 17.5
>
But
by( data.frame(data,weights), groups, function(d) { weighted.mean(d[,1],
d[,2]) } )
does the right thing
groups: 1
[1] 5
------------------------------------------------------------
groups: 2
[1] 6
>
Bert Gunter wrote:
>
> ?by
>
> Bert Gunter
> Genentech Nonclinical Statistics
>
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