David Winsemius
On Jan 12, 2009, at 10:52 AM, Steve Murray wrote:
>
> Dear all,
>
>
>
> I have a dataframe of 3 columns, consisting of 'longitude', 'latitude'
> and a corresponding 'value'. Where identical 'longitude' and
> 'latitude'
> pairs occur more than once, I want their corresponding 'value' to be
> summed and the 'pair' to only appear once.
>
>
>
> For example:
>
>
>
> long lat value
>
> 10 20 5
>
> 6 2 3
>
> 27 -3 9
>
> 10 20 10
>
> 4 -1 0
>
> 6 2 9
>
>
>
>
>
> would be converted to something like:
>
>
>
> long lat value
>
>
> 10 20 15
>
>
> 6 2 12
>
>
> 27 -3 9
>
>
> 4 -1 0
>
>
>
>
>
>
> ...as rows 1 and 4, 2 and 6 respectively are matched with respect to
> the 'long' and 'lat' columns. Their values in column 3 are then summed
> and reported as one row in the new dataframe.
>
>
>
> How would I go about coding this in R?
>
>
>
> Many thanks,
>
>
>
> Steve
>
>
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