Kathi - 1 year ago 93
R Question

# Calculating number of points within a certain radius

Given a data frame with latitudes and longitudes I want to add a column that simply contains the count of other points (of the same data frame) that are within a certain radius e.g. within 10 km of that specific point.

Example data:

``````set.seed(1)
lat<-runif(10,-90,90)
long<-runif(10,-180,180)
id<-1:10
dat<-cbind(id,lat,long)

id       lat         long
[1,]  1 -42.20844 -105.8491530
[2,]  2 -23.01770 -116.4395691
[3,]  3  13.11361   67.3282248
[4,]  4  73.47740  -41.7226614
[5,]  5 -53.69725   97.1429112
[6,]  6  71.71014   -0.8282728
[7,]  7  80.04155   78.3426630
[8,]  8  28.94360  177.0861941
[9,]  9  23.24053  -43.1873354
[10,] 10 -78.87847   99.8802797
``````

Now given the radius variable I want a new column say "X" that for each point only contains the number of other points that are within "radius". I do not care about which points these are.

While this R - Finding closest neighboring point and number of neighbors within a given radius, coordinates lat-long topic and answer get close it does not solve the specific question of the simple count. This question is different as I need the counts of all points within the radius and not the points

Try this:

``````library(geosphere)
cbind(dat, X=rowSums(distm (dat[,3:2],
fun = distHaversine) / 1000 <= 10000)) # number of points within distance 10000 km

id       lat         long X
[1,]  1 -42.20844 -105.8491530 5
[2,]  2 -23.01770 -116.4395691 5
[3,]  3  13.11361   67.3282248 5
[4,]  4  73.47740  -41.7226614 6
[5,]  5 -53.69725   97.1429112 4
[6,]  6  71.71014   -0.8282728 6
[7,]  7  80.04155   78.3426630 6
[8,]  8  28.94360  177.0861941 5
[9,]  9  23.24053  -43.1873354 6
[10,] 10 -78.87847   99.8802797 4
``````
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