find locations within certain lat/lon distance in r

Question

I have a gridded dataset, with data available at the following locations:

lon <- seq(-179.75,179.75, by = 0.5)
lat <- seq(-89.75,89.75, by = 0.5)
         


        

Answer 1

Just use hutils::haversine_distance(lat, lon, mylat, mylon) < 500 directly.

If the points are assumed to be a cross join of the given lat and lon, use a cross-join first to obtain them:

library(data.table)
library(hutils)

lon <- seq(-179.75,179.75, by = 0.5)
lat <- seq(-89.75,89.75, by = 0.5)

mylat <- 47.9625
mylon <- -87.0431

Points <- CJ(lon = lon,
             lat = lat)
Points[, dist := haversine_distance(lat, lon, mylat, mylon)]
Points[, sum(dist < 500)]
#> [1] 379

^{Created on 2019-10-24 by the reprex package (v0.3.0)}

It improves on the existing answers by its speed and robustness. In particular, it does not rely on the gridded nature of the data and will work with long vectors of coordinates. Below are timings for 100,000 points

# A tibble: 2 x 14
  expression         min        mean      median         max `itr/sec`  mem_alloc  n_gc n_itr  total_time
                                    
1 nicola2    39891.120ms 39891.120ms 39891.120ms 39891.120ms    0.0251 8808.632MB     0     1 39891.120ms
2 hutils        15.492ms    15.591ms    15.578ms    15.728ms   64.1       5.722MB     0    33   514.497ms