Script for converting latitude and longitude coordinates (e.g., from Qualtrics) into country codes using R

longlat2countr.r

# Script for converting latitude and longitude coordinates (e.g., from Qualtrics) into country codes using R
# Assumes data set is called rcases

# country from coords
library(sp)
# install.packages("rworldmap")
library(rworldmap)

# The single argument to this function, points, is a data.frame in which:
#   - column 1 contains the longitude in degrees
#   - column 2 contains the latitude in degrees
coords2country = function(points)
{  
    # https://stackoverflow.com/a/14342127/180892
  countriesSP <- getMap(resolution='low')
  #countriesSP <- getMap(resolution='high') #you could use high res map from rworldxtra if you were concerned about detail

  # convert our list of points to a SpatialPoints object

  # pointsSP = SpatialPoints(points, proj4string=CRS(" +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"))

  #setting CRS directly to that from rworldmap
  pointsSP = SpatialPoints(points, proj4string=CRS(proj4string(countriesSP)))  


  # use 'over' to get indices of the Polygons object containing each point 
  indices = over(pointsSP, countriesSP)

  # return the ADMIN names of each country
  indices$ADMIN  
  #indices$ISO3 # returns the ISO3 code 
  #indices$continent   # returns the continent (6 continent model)
  #indices$REGION   # returns the continent (7 continent model)
}


rcases$locationlatitude <- as.numeric(rcases$locationlatitude)
rcases$locationlongitude <- as.numeric(rcases$locationlongitude)


rcases$ipcountry <- coords2country(rcases[, c("locationlongitude", "locationlatitude" )])
rcases$ipcountry <- as.character(rcases$ipcountry)