[R] weighting means

[Oscar Rueda]

Hello to all

Is there a way to get weighted means using summary.formula() from Hmisc?

For example, the following doesn't work:

>a<-c(rep("A",3),rep("B",7))
>b<-c(1:10)
>c<-c(rep("X",2),rep("Y",8))
>w<-c(10:1)
>z<-data.frame(a,b,c,w)
>library(Hmisc)
>summary(b~a+c,data=z,method="cross",fun=function(y)wtd.mean(y,weights=z$w))

Error in wtd.mean(y, weights = z$w) : dim<- length of dims do not match the length of object

Thanks for the replies,

Oscar Rueda



22/08/02 1:16:15, Frank E Harrell Jr <fharrell at virginia.edu> escribió:

>On Wed, 21 Aug 2002 12:10:44 -0400
>kjetil halvorsen <kjetilh at umsanet.edu.bo> wrote:
>
>> 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
>> > 
>> > --
>> > Tim Wilson      |   Visit Sibley online:   | Check out:
>> > Henry Sibley HS |  http://www.isd197.org   | http://www.zope.com
>> > W. St. Paul, MN |                          | http://slashdot.org
>> > wilson at visi.com |  <dtml-var pithy_quote>  | http://linux.com
>
>Also take a look at the many weighted stats functions in the Hmisc library.  Do 
>library(Hmisc)
>?wtd.mean
>
>-Frank
>
>-- 
>Frank E Harrell Jr              Prof. of Biostatistics & Statistics
>Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
>U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat
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