choropleth_sp.R

# FUNCTION TO CREATE A CHOROPLETH MAP USING SPPLOT
choropleth_sp <- function(.poly, id1, .df = .poly@data, id2 = id1, field, 
                          .title = "", .legtitle = "Values", colpal = 'PuRd', ...){
                            
     # load required libraries
     library(maptools); library(spatial); library(RColorBrewer);
     library(classInt); library(ggplot2); gpclibPermit();
                            
     # create id to match shapefile with data
     id1 = llply(id1, as.name); 
     id2 = llply(id2, as.name);
     .poly@data$id = with(.poly@data, do.call('paste', c(id1, sep = "-")));
     .df$id        = with(.df,        do.call('paste', c(id2, sep = "-")));
     
      # merge with data
      map.data = merge(.poly@data, .df);
      
      # choose breaks and fill colours
      map.data.m  = melt(map.data, measure.vars = field);
      breaks      = do.call("classIntervals", list(var = map.data.m$value, ...))$brks;
      # map.data  = within(map.data, {value = cut(value, breaks, incl = T)});
      
      # plot choropleth map
      # map.data  = data.frame(cast(map.data, id ~ variable));
      colors    = brewer.pal(length(breaks) - 1, colpal);
     .poly@data = map.data[match(.poly@data$id, map.data$id),];
       
      p1 = spplot(.poly, field, at = breaks, col.regions = colors, col = 'transparent',
                   main = .title);
           
      return(p1)
}

# FUNCTION TO READ SHAPE FILE FROM A ZIPPED FOLDER
readShapeZip <- function(url, .tempfile = tempfile(), 
                  .tempdir = tempdir()){
   require(maptools); gpclibPermit();
   download.file(url = url, .tempfile, quiet = T);
  .files    = unzip(.tempfile, exdir = .tempdir);
  .shpfile  = head(.files)[grep('shp', head(.files))];
  .poly     = readShapeSpatial(.shpfile);
   return(.poly)
}