weighting means

Wed, Aug 21, 2002 7:12 AM

Not sure if this is what you're looking for.  Try something like

 by(faculty, faculty$FACULTY, function(Q8, CETP) weighted.mean(Q8, CETP))

Andy

-----Original Message-----
From: Tim Wilson [mailto:wilson at visi.com]
Sent: Tuesday, August 20, 2002 4:35 PM
To: R-help
Subject: [R] weighting means

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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