Listing number of obervations by location

Question

Need help here. I am trying to create a new column that will list the number of restaurants with in 200 meters of a restaurant using latitude and longitude. I couldn\'t find any

Answer 1

One approach would be to compute the distance matrix, and then to figure out the ones that are sufficiently close (here I demonstrate being within 20 kilometers so the numbers aren't all 0):

# Load the fields library
library(fields)

# Create a simple data frame to demonstrate (each row is a restaurant). The rdist.earth function
# we're about to call takes as input something where the first column is longitude and the second
# column is latitude.
df = data.frame(longitude=c(-111.9269, -111.8983, -112.1863, -112.0739, -112.2766, -112.0692),
                latitude=c(33.46337, 33.62146, 33.65387, 33.44990, 33.56626, 33.48585))

# Let's compute the distance between each restaurant.
distances = rdist.earth(df, miles=F)
distances

#          [,1]     [,2]     [,3]         [,4]     [,5]         [,6]
# [1,]  0.00000 17.79813 32.07533 1.373515e+01 34.41932 1.344867e+01
# [2,] 17.79813  0.00000 26.93558 2.510519e+01 35.61413 2.189270e+01
# [3,] 32.07533 26.93558  0.00000 2.498676e+01 12.85352 2.162964e+01
# [4,] 13.73515 25.10519 24.98676 1.344145e-04 22.84310 4.025824e+00
# [5,] 34.41932 35.61413 12.85352 2.284310e+01  0.00000 2.122719e+01
# [6,] 13.44867 21.89270 21.62964 4.025824e+00 21.22719 9.504539e-05

# Compute the number of restaurants within 20 kilometers of the restaurant in each row.
df$num.close = colSums(distances <= 20) - 1
df$num.close
# [1] 3 1 1 2 1 2