Al,

Is there any "ID" index for the pairs? For example, if the first pair can be
labeled "a", and second pair labeled "b" etc., then you can add an index
column or you may already have such a column in your list. Then run
aggregate(your.data.column, by=index.column, FUN=mean). Or you can just add
an extra index column anyway rep(1:number of the rows/2, each=2). Hope this
helps.

-- 
Jun Shen PhD
PK/PD Scientist
BioPharma Services
Millipore Corporation
15 Research Park Dr.
St Charles, MO 63304
Direct: 636-720-1589

On Tue, Mar 31, 2009 at 10:40 AM, Alan O'Loughlin <OLougA@wyeth.com> wrote:

> Hello,
>
> I'm trying to create a for loop for a data set, I have a list of results in
> this data set and I want to take the 1st two add them together and divide by
> the mean of the 1st to, then do the same for the 3rd and 4th values in the
> list and so on and each time return a value for the calculation on each
> pair.
>
> Any help would be appreciated.
>
> Thanks,
> Al
>
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