I have two shape-files; one is a point file (some information for world) and the other is a 21-countries shape-file.
I need to extract the points which falls with in a country. I have to repeat this step in 21 times in QGIS or ArcGIS.
Is there any way to do this in R and if is in batch processing, that would be really great as I have to repeat this for other 4 data sets as well. Thanks in advance
So as an example how to use over() consider the following simulated data.
library(raster)
library(sp)
#generate point distribution | with (x,y) coordinates
set.seed(42);pts <- SpatialPoints(data.frame(x = runif(30, 1, 5), y = runif(30, 1, 5)))
#create polygons
df<-data.frame(X = c(rep(1,5),rep(2,5),rep(3,5),rep(4,5),rep(5,5)),
Y = c(rep(seq(1,5,1),5)))
df$cell<-1:nrow(df) #polygon identifier (for later)
#make into spatial object (probably better way to do this)
coordinates(df) <- ~X+Y
rast <- raster(extent(df), ncol = 5, nrow = 5)
grid<-rasterize(df, rast, df$cell, FUN = max)
grid<-rasterToPolygons(grid) #create polygons
#plot to check
plot(grid); points(pts)
#and extract
pointsinpolygon = over(SpatialPolygons(grid@polygons), SpatialPoints(pts))
The last bit you can also do as
df$pointsinpolygon <- over(SpatialPolygons(grid@polygons), SpatialPoints(pts))
to write the results directly to the dataframe.