This may do it but I have not verified the figures.
library(cwhmisc)
by(xx[,3:4],xx[,2],function(x,y) weighted.mean(x,y))
--- On Thu, 7/30/09, Kirsten Beyer <kirsten-be...@uiowa.edu> wrote:
> From: Kirsten Beyer <kirsten-be...@uiowa.edu>
> Subject: [R] weight median by count for multiple records
> To: r-help@r-project.org
> Received: Thursday, July 30, 2009, 1:58 PM
> Hello everyone,
>
> I have a .csv file with the following format:
>
> uniqueID SubjectID
> Distance_miles Tag
> 1
> 1001
> 5.5
> 3
> 2
> 1001
> 7
> 1
> 3
> 1001
> 6.5
> 1
> 4
> 1001
> 5
> 1
> 5
> 1002
> 2
> 2
> 6
> 1002
> 2
> 2
> 7
> 1002
> 1.5
> 2
> 8
> 1003
> 15
> 2
> 9
> 1003
> 17
> 2
> 10
> 1003
> 18
> 2
>
>
> For each SubjectID, I want to calculate the median
> distance, where the
> Tag variable indicates the number of times that distance
> was recorded.
> My final output table would be...
>
> SubjectID Median Distance
> 1001
> 5.5
> 1002
> 2
> 1003
> 17
>
> I have used the following script to calculate the median
> for a data
> frame where each recorded distance has its own row, and
> where temp is
> a dataframe containing each unique SubjectID and routes is
> the file I
> describe above.
>
> for(i in 1:nrow(temp)){
> temp$mediandistance[i] <-
> median(routes$Distance_miles[routes$Subject_ID==temp$Subject_ID[i]])
> }
>
> I am interested to know...
> (1) Is there a way to incorporate a weighted median into
> this script,
> where the weights are the number of times each distance is
> recorded?
> (2) Can I transform my current matrix into one that gives
> each
> distance its own row?
>
> Help is much appreciated,
> Kirsten Beyer
>
> ______________________________________________
> R-help@r-project.org
> mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained,
> reproducible code.
>
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