[R] Join data by minimum distance

[Roy Mendelssohn]

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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NOAA/NMFS
Environmental Research Division
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