Hi Monica:
On Sep 12, 2008, at 11:59 AM, Monica Pisica wrote:
I am wondering if there is a function which will do a join between 2
data.frames by minimum distance, as it is done in ArcGIS for
example. For people who are not familiar with ArcGIS here it is an
explanation:
Suppose you have a data.frame with x, y, coordinates called track,
and a second data frame with different x, y coordinates and some
other attributes called classif. The track data.frame has a
different number of rows than classif. I want to join the rows from
classif to track in such a way that for each row in track I add only
the row from classif that has coordinates closest to the coordinates
in the track row (and hence minimum distance in between the 2 rows),
and also add a new column which will record this minimum distance.
Even if the coordinates in the 2 data.frames have same name, the
values are not identical between the data.frames, so a merge by
column is not what I am after.
I did an R Site Search but nothing related to this particular type
of join emerged.
Have you looked at the package "field". It has distance functions.
You would then have to do a little programming to find the minimum
distance and add the columns.
HTH,
-Roy M.
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Roy Mendelssohn
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