Hi,

you have to use tapply().  A small example:

> region <- c("Atl", "Mount", "Atl")
> state <- c("NY", "AR", "WAS")
> pop <- c(1000, 100, 1000)
> d <- data.frame(region,state,pop)
	# note that region and state are coerced to factors by data.frame()
> tapply(d$pop, d$region, sum)
  Atl Mount
 2000   100

A very similar example was in ,,An introduction to R'' for version 1.1, I
think it is in the current version too.


best wishes,

Ott Toomet




On Wed, 23 Jan 2002, Erin Hodgess wrote:

> Dear R People:
>
> Here is a very simple question, please:
>
> I have a data frame with the state name, state division, and population.
>
> Note: state division is something like Atlantic, Mountain, etc.
>
> I want to produce a table with the state division and the total of the
> populations for the states within that division.
>
> I've been messing with "table" but so far, no luck.
>
> This is R1.3.1, on Windows 98.
>
> thanks in advance!
>
> Sincerely,
> Erin Hodgess
> Associate Professor
> Department of Computer and Mathematical Sciences
> University of Houston - Downtown
> 1 Main Street
> Houston, TX 77002
> mailto: hodgess@uhddx01.dt.uh.edu
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