try aggregate(), e.g.,
dat <- read.table(textConnection("long lat value
10 20 5
6 2 3
27 -3 9
10 20 10
4 -1 0
6 2 9"), header = TRUE)
closeAllConnections()
aggregate(dat["value"], list(Long = dat$long, Lat = dat$lat), sum)
I hope it helps.
Best,
Dimitris
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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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus Medical Center
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
______________________________________________
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and provide commented, minimal, self-contained, reproducible code.
