Country names from coordinates

Here is an approach using raster::extract(). I assume your point locations 
are unprojected.

library(raster)
library(tmap)

data(World)
proj4string(World)
# [1] "+proj=eck4 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m 
+no_defs +towgs84=0,0,0"

pts <- SpatialPointsDataFrame(temp [, c(1,2)], temp, 
proj4string=CRS("+init=epsg:4326"))
# Reproject World
World <- spTransform(World, CRS("+init=epsg:4326"))
# Extract and append World attributes at pts point locations
pts <- extract(World, pts, sp=TRUE)

--Mel.


On 7/25/2016 9:01 AM, Miluji Sb wrote:

 I have the following data at 0.5 degree by 0.5 degree.

 temp <- dput(head(ptsDF,10))
 structure(list(longitude = c(-68.25, -67.75, -67.25, -68.25,
 -67.75, -67.25, -71.25, -70.75, -69.25, -68.75), latitude = c(-54.75,
 -54.75, -54.75, -54.25, -54.25, -54.25, -53.75, -53.75, -53.75,
 -53.75), GDP = c(1.683046, 0.3212307, 0.0486207, 0.1223268, 0.0171909,
 0.0062104, 0.22379, 0.1406729, 0.0030038, 0.0057422)), .Names =
 c("longitude",
 "latitude", "GDP"), row.names = c(4L, 17L, 30L, 43L, 56L, 69L,
 82L, 95L, 108L, 121L), class = "data.frame")

 I would like add the corresponding country names to each of the
 coordinates. This is what I have done:

 library(data.table)
 library(rgdal)
 library(reshape2)
 library(dplyr)
 library(tidyr)
 library(lubridate)
 library(maps)
 library(countrycode)
 library(ggplot2)
 library(raster)

 coord_cells <-temp [,c(1,2)]
 pts_cells <-
 SpatialPoints(coord_cells,proj4string=CRS(proj4string(worldmap)))
 indices_cells <- over(pts_cells, worldmap,na.rm=TRUE)
 foo_cells<-indices_cells[,c(3,5)] # Keep ISO3 and country names only
 new_data <- cbind(foo_cells, temp)

 However, I get a large number of NAs for coordinates which should have
 corresponding countries. What am I doing wrong? Any suggestions? Thank
 you.

 Sincerely,

 Milu

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