[R] weighting means

[kjetil halvorsen]

What about:

> ?weighted.mean
> ?tapply
> Q8 <- rnorm(100)
> Faculty <- factor(c(rep(1,50), rep(2,50)))
> w <- 1:100
> tapply(Q8, Faculty, weighted.mean, w)
         1          2 
-0.0976302 -0.1457895 


Kjetil Halvorsen

Tim Wilson wrote:
> 
> Hi everyone,
> 
> I've got a dataframe called 'faculty'. I want to do a weighted mean on
> the column called 'Q8' weighted by the contents of column 'CETP'. In
> addition, I need to operate on the result of splitting 'faculty'
> according to the contents of a column 'FACULTY'. For example
> 
> > lapply(split(faculty$Q8, faculty$FACULTY), mean)
> $"1"
> [1] 2.2
> 
> $"2"
> [1] 1.888889
> 
> gives the mean of 'Q8' after splitting by 'FACULTY'. When I try this
> with weighted.mean, it doesn't work because I don't know how to specify
> the result of the split as the argument for weighted.mean. For example,
> 
> > lapply(split(faculty$Q8, faculty$FACULTY), weighted.mean)
> $"1"
> [1] 2.2
> 
> $"2"
> [1] 1.888889
> 
> gives the same results as above because I haven't specified the vector
> to use for weighting. The following doesn't work at all for the obvious
> reason that weighted.mean is not operating on the result of the split.
> 
> > lapply(split(faculty$Q8, faculty$FACULTY), weighted.mean(faculty$Q8,
> faculty$CETP))
> Error in match.fun(FUN) : not function, character, or symbol:
> "weighted.mean(faculty$Q8, faculty$CETP)"
> >
> 
> Any ideas?
> 
> -Tim
> 
> --
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