R help - Aug 2007 - by group problem

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

	[[alternative HTML version deleted]]

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
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

See the examples labelled head in the examples section near the bottom of:

http://sqldf.googlecode.com/svn/trunk/man/sqldf.Rd

These show show to do it using order as well as using SQL via sqldf.

On 8/31/07, Cory Nissen <cnissen at akoyainc.com>
wrote:
> 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
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Perhaps you want this?

data <- NULL
data$state <- c(rep("Illinois", 10), rep("Wisconsin",
10))
data$county <- c("Adams", "Brown", "Bureau",
"Cass", "Champaign",
                 "Christian", "Coles", "De Witt",
"Douglas", "Edgar",
                 "Adams", "Ashland", "Barron",
"Bayfield", "Buffalo",
                 "Burnett", "Chippewa", "Clark",
"Columbia", "Crawford")
data$percentOld <- c(17.554849, 16.826594, 18.196593, 17.139242,  8.743823,
                     17.862746, 13.747967, 16.626302, 15.258940, 18.984435,
                     19.347022, 17.814436, 16.903067, 17.632781, 16.659305,
                     20.337817, 14.293354, 17.252820, 15.647179, 16.825596)

data<-data.frame(data,stringsAsFactors=FALSE)
rankWithinState<-unlist(tapply(-data$percentOld,data$state,rank))
names(rankWithinState)<-NULL
data<-data.frame(data,rankWithinState)
highCounties<-data[data$rankWithinState<=5,]
highCountiesSorted<-highCounties[order(highCounties$state,-highCounties$percentOld),]

Cory Nissen wrote:
> 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
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