The goal of withinr package is to find a location index within a certain Radius and a closest location. You can use withinr function and closestr in this package. You need to rename column 'latitude' to 'lat' and 'longitude' to 'lon'. Distance unit is meter(m).
You can install withinr like so:
devtools::install_github("bominkm/withinr")This is a basic example which shows you how to solve a common problem:
library(withinr)
df_sample <- data.frame(lon = c(128.1, 128, 128.6, 135), lat = c(37, 37.1, 37.5, 42))
withinr(128, 37, df_sample, 15000)
closestr(128, 37, df_sample)