[R] Odp: by group problem

[Petr PIKAL]

Hi

> I am working with census data.  My columns of interest are...
> 
> PercentOld - the percentage of people in each county that are over 65
> County - the county in each state
> State - the state in the US
> 
> There are about 3100 rows, with each row corresponding to a county 
within a state.
> 
> I want to return the top five "PercentOld" by state.  But I want the 
County 
> and the Value.
> 
> I tried this...
> 
> topN <- function(column, n=5)
>   {
>     column <- sort(column, decreasing=T)
>     return(column[1:n])
>   }
> top5PerState <- tapply(data$percentOld, data$STATE, topN)

Try

aggregate(data$PercentOld, list(data$State, data$County), topN)

Regards
Petr


> 
> But this only returns the value for "percentOld" per state, I also want 
the 
> corresponding County.
> 
> I think I'm close, but I just can't get it...
> 
> Thanks
> 
> cn
> 
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> 
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