One of undoubtedly many ways:
# kind of a pain to delete the blank rows. Try to give us full example
next time?
> txt<- "long lat value
+ 10 20 5
+ 6 2 3
+ 27 -3 9
+ 10 20 10
+ 4 -1 0
+ 6 2 9
+ "
> DF2 <- read.table(textConnection(txt), header=TRUE)
> DF3 <- data.frame(with(DF2,list(lon=long, lat=lat,
value=ave(value,long, lat, FUN=sum))))
> DF3
lon lat value
1 10 20 15
2 6 2 12
3 27 -3 9
4 10 20 15
5 4 -1 0
6 6 2 12
If you want the column name to be "long", the fix is obvious.
--
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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