rm(list=ls())
setwd("H:/lab2")

# load the spdep library
library(spdep)

###### POLYGON SHAPEFILE

## example shapefile: columbus.shp

# import your shapefile using readShapePoly
shape <- readShapePoly("columbus.shp",IDvar="POLYID")

# read-in the table containing the data the you want to add to your shapefile
  # make sure that the table contains a column with a unique identifier corresponding to IDvar
tab <- read.table("join_example.txt",header=TRUE)

# creates a vector of all polygon IDs
  #note that it is the "character" version of POLYID (in this example)
shpID <- sapply(slot(shape,"polygons"),function(x) slot(x,"ID"))

# make the ID variable from the data table into class "character"
tabID <- as.character(tab$ID)

# match the two unique identifiers
  # match() needs both its arguments to be of the same class. Here: "character"
  
  #### if you want to keep all polygons
    tab <- tab[match(shpID,tabID),]
      # matches both IDs and replaces nomatch values by NA
    rownames(tab) <- shpID
    shape.mod <- spCbind(shape,tab)
    
  #### if you want to delete polygons with no matching data in the table
    #tab <- tab[shpID%in%tabID,]
    #shape.mod <- shape.mod[shpID%in%tabID,]
      # matches and removes the non-matching locations from the table and the original shapefile
    #shape.mod <- spCbind(shape.mod,tab)

shape.mod@data
# writes a new shapefile in the current working directory
writePolyShape(shape.mod,"shape_mod")

# this is an alternative way of exporting the shapefile
# it requires the library rgdat and seems to create a "cleaner" shapefile in the sense that the .dbf file contains one less column
  # library(rgdal)
  #writeOGR(shape.mod,dsn=".",layer="shape_mod",driver="ESRI Shapefile")



###### POINT SHAPEFILE

## example shapefile: pitt93.shp

# import your shapefile using readShapePoly
shape <- readShapePoints("pitt93.shp")

# read-in the table containing the data the you want to add to your shapefile
  # make sure that the table contains a column with a unique identifier corresponding to IDvar
tab <- read.table("join_example_pitt.csv",header=TRUE,sep=",")

# match the two unique identifiers
   # match() needs both its arguments to be of the same type. Here: "numeric"

  #### if you want to keep all points
    tab <- tab[match(shape$NEWID,tab$ID),]
      # matches both IDs and replaces nomatch values by NA
    rownames(tab) <- shape$NEWID
    shape.mod <- spCbind(shape,tab)
    
  #### if you want to delete points with no matching data in the table
    #tab <- tab[shape$NEWID%in%tab$ID,]  
    #shape.mod <- shape.mod[shape$NEWID%in%tab$ID,]
      # matches and removes the non-matching locations from the table and the original shapefile
    #shape.mod <- spCbind(shape.mod,tab)

shape.mod@data
# writes a new shapefile in the current working directory
writePointsShape(shape.mod,"shape_mod")