merging df with world map

On Jun 17, 2016, at 1:06 PM, ch.elahe via R-help <r-help at r-project.org> wrote:

Hi all,
I want to use world map in ggplot2 and show my data on world map. my df is:


   $ COUNTRY           : chr  "DE" "DE" "FR" "FR" ..

   $ ContrastColor     : int  9 9 9 9 13 9 9 9 9 ..

   $ quant             : Factor w/ 4 levels "FAST","SLOW",..I need to merge my df with world_map data which is like this:


   world_map=map_data("world")
   data.frame':   99338 obs. of  6 variables:
   $ long     : num  -69.9 -69.9 -69.9 -70 -70.1 ...
   $ lat      : num  12.5 12.4 12.4 12.5 12.5 ...
   $ group    : num  1 1 1 1 1 1 1 1 1 1 ...
   $ order    : int  1 2 3 4 5 6 7 8 9 10 ...
   $ region   : chr  "Aruba" "Aruba" "Aruba" "Aruba" ...
   $ subregion: chr  NA NA NA NA ...
but by merging my df with world map data I get a data frame with zero observation in it,I use this command for merging:


   world_map=merge(world_map,df,by.x="region",by.y="COUNTRY")
   str(world_map) 

   'data.frame':   0 obs. of  133 variables:
   $ region            : chr 
   $ long              : num 
   $ lat               : num 
   $ group             : num 
   $ order             : int 
   $ subregion         : chr
does anyone know what is the problem of this merging that I am currently using?
thanks for any help!