[R] separation depending on equal contents in more than one field

[Florian Jansen]

Hi,

I have a dataframe:

(obs <- data.frame(a=c(1,2,2,3,3,3), b=c(1,2,3,4,4,5), c=1:2))
attach(obs)

In reality its about 1 million rows.

Some of the datasets have same contents in col a and! b like row 4 and 5.
I want to do some calculations on col c within the duplicated rows and 
merge them afterwards:

layer <- function(x) round((1-prod(1-x/100))*100,0)
(covnew <- aggregate(c, list(a=a, b=b), layer))

This works fine, but not with 1 mill. rows because of memory space 
limitations.
So I thought to split the dataframe into the majority of unique rows on 
one hand and all duplicated rows on the other:

With
subset(obs, a %in% a[duplicated(a)])
and !a respectively this works fine for single column comparison.
This must be also possible for two column comparison, but I can`t get it.

Thanks
Florian

-- 
Dr. Florian Jansen
Geobotany & Nature Conservation
Institute for Botany and Landscape Ecology
Ernst-Moritz-Arndt-University
Grimmer Str. 88
17487 Greifswald - Germany
+49 (0)3834 86 4147