[datatable-help] stratified weighted means

[Matthew Dowle]

Deja vu?!

http://stackoverflow.com/a/13454651/403310

https://r-forge.r-project.org/tracker/index.php?func=detail&aid=2381&group_id=240&atid=975


On 19.12.2012 17:31, David Freedman wrote:
> I apologize for the simple question, but something that worked in v 
> 1.8.4
> fails in v 1.8.6 - it involves getting stratified weighted means from 
> a data
> table.  The code is
>
> library(data.table)
> (dt <- data.table(id     = rep(c(1,2), each=9),
>                  month  = rep(100L:108L, times=2),
>                  value=rnorm(18),
>                  swt=sample(1:18,18) ))
>
> dt[,lapply(.SD,mean),keyby=list(id)] #fine - stratified means
> dt[,lapply(.SD,function(x)weighted.mean(x,swt))] #fine - overall 
> weighted
> mean
> dt[,lapply(.SD,function(x)weighted.mean(x,swt)),keyby=list(id)] 
> #fails
> 'object "swt" not found'
>
> I'm using v 1.8.6 of data.table, and I am sure that this statement 
> for
> calculating stratified weight means worked in v 1.8.4.
>
> Output of sessionInfo is:
> R version 2.15.2 (2012-10-26)
> Platform: i386-w64-mingw32/i386 (32-bit)
>
> locale:
> [1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United
> States.1252
> [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
>
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] data.table_1.8.6
>
> loaded via a namespace (and not attached):
> [1] tools_2.15.2
>
> Any help would be greatly appreciated as this is something I do 
> almost
> daily.
>
> And I realize that I could always use something like
> dt[,list(wm(month,swt),wm(value,swt)),keyby=list(id)]
> But this becomes difficult if I want the stratified weighted means 
> for a
> large number of variables
>
> thanks, david freedman
>
>
>
>
>
>
> --
> View this message in context:
> 
> http://r.789695.n4.nabble.com/stratified-weighted-means-tp4653556.html
> Sent from the datatable-help mailing list archive at Nabble.com.
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