Reproject longitude and latitude to OSGB grid using {sf} and produce a column referring to unique 1km grid squares

lonlat_to_1km_grid.R

#load pacakges
library(sf)
library(magrittr) #for the pipe

#create a test dataframe
test <- expand.grid(latitude = 50:52,longitude = -1:1)

#load as sf, transform, round to 1km
test2 <- st_as_sf(test,coords =c("longitude","latitude"),crs = 4326) %>% 
  st_transform(27700) %>% 
  st_coordinates() %>% #extract the coordinages
  round(digits = -3) %>%  #to 1km, use digits = -2 for 100m
  data.frame()

#create a pseudo grid square reference (it doesn't ahve the two letters but it is unique for each 1km grid square)
test2$km_grid <- paste0(test2$X,test2$Y)