[R-sig-Geo] Country names from coordinates

[Miluji Sb]

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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