[R] by group problem

Cory Nissen
Fri, 31 Aug 2007 13:08:47 -0000

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)

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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