Manipulate shapefile attribute table using R

RichT picture RichT · Jun 22, 2013 · Viewed 10.4k times · Source

I've posted this question on the GIS stack exchange, but it's not seeing much traffic.

I'm a GIS user who's been using R for stats for a few years, and I'm excited to see a lot of new GIS capabilities being released (raster, shapefiles, rgdal, etc).

I've done a lot of database and table manipulation in R, so being able to add and remove attributes from shapefiles is a powerful potential.

I'm hoping I'm just missing what's out there, but I can't seem to find a good method for adding or removing attributes from a shapefile attribute table.

Can anyone from Overflow respond to my GIS post? Or can I be advised how to get my list attribute table into a dataframe and back to replace the current attribute table?

Edit progress

Some progress since my original post:

This is getting at figuring out how to take my attribute table appart (.dbf), add stuff, and now I'm trying to put it back together to replace the original dbf.

>libary(raster); library(rgdal); library(shapefiles)
>shp<-shapefile(Shape)  # D.C. area airport polygons
>summary(shp)           #Shapefile properties

Object of class SpatialPointsDataFrame
Coordinates:
                min       max
coords.x1  281314.2  337904.7
coords.x2 4288867.0 4313507.0
Is projected: TRUE 
proj4string :
[+proj=utm +zone=18 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0]
Number of points: 4
Data attributes:
    ObjectID        LOCID               NAME              FIELD              STATE            STATE_FIPS           ACAIS              TOT_ENP            TYPE          
 Min.   :134.0   Length:4           Length:4           Length:4           Length:4           Length:4           Length:4           Min.   :    271   Length:4          
 1st Qu.:242.8   Class :character   Class :character   Class :character   Class :character   Class :character   Class :character   1st Qu.:   3876   Class :character  
 Median :339.0   Mode  :character   Mode  :character   Mode  :character   Mode  :character   Mode  :character   Mode  :character   Median :3409113   Mode  :character  
 Mean   :310.0                                                                                                                     Mean   :3717251                     
 3rd Qu.:406.2                                                                                                                     3rd Qu.:7122488                     
 Max.   :428.0

 >shp.AT<-read.dbf(gsub(".shp", ".dbf", Shape), header=TRUE)    #Read in the attribute table from the .dbf
 > shp.AT       # First object in the dbf looks like an attribute table!
$dbf
  ObjectID LOCID                            NAME               FIELD    STATE STATE_FIPS ACAIS TOT_ENP          TYPE
1      134   ADW                     Andrews AFB                <NA> Maryland         24     Y    5078      Military
2      279   DCA             Washington National                <NA> Virginia         51     Y 6813148          <NA>
3      399   HEF               Manassas Regional Harry P Davis Field Virginia         51     Y     271      Regional
4      428   IAD Washington Dulles International                <NA> Virginia         51     Y 8050506 International

$header
$header$file.version
[1] 3

$header$file.year
[1] 113

$header$file.month
[1] 4

$header$file.day
[1] 12

$header$num.records
[1] 4

$header$header.length
[1] 321

$header$record.length
[1] 148

$header$fields
        NAME TYPE LENGTH DECIMAL
1   ObjectID    N     10       0
2      LOCID    C      5       0
3       NAME    C     45       0
4      FIELD    C     30       0
5      STATE    C     24       0
6 STATE_FIPS    C      2       0
7      ACAIS    C      1       0
8    TOT_ENP    N     11       0
9       TYPE    C     20       0

>shp.tab<-as.data.frame(shp.AT[1]) # Grab the first object of the .dbf as a data.frame

> shp.tab       # First list object
  dbf.ObjectID dbf.LOCID                        dbf.NAME           dbf.FIELD dbf.STATE dbf.STATE_FIPS dbf.ACAIS dbf.TOT_ENP      dbf.TYPE
1          134       ADW                     Andrews AFB                <NA>  Maryland             24         Y        5078      Military
2          279       DCA             Washington National                <NA>  Virginia             51         Y     6813148          <NA>
3          399       HEF               Manassas Regional Harry P Davis Field  Virginia             51         Y         271      Regional
4          428       IAD Washington Dulles International                <NA>  Virginia             51         Y     8050506 International 

> shp.tab$NewAT<-1:nrow(shp.tab) # Add my new attribute

> shp.tab # Added my new attribute, now to get this back into my shapefile
  dbf.ObjectID dbf.LOCID                        dbf.NAME           dbf.FIELD dbf.STATE dbf.STATE_FIPS dbf.ACAIS dbf.TOT_ENP      dbf.TYPE NewAT
1          134       ADW                     Andrews AFB                <NA>  Maryland             24         Y        5078      Military     1
2          279       DCA             Washington National                <NA>  Virginia             51         Y     6813148          <NA>     2
3          399       HEF               Manassas Regional Harry P Davis Field  Virginia             51         Y         271      Regional     3
4          428       IAD Washington Dulles International                <NA>  Virginia             51         Y     8050506 International     4

>write.dbf(shp.tab, gsub(".shp", ".dbf", Shape)) # Knew this wouldn't work, but demonstrate attempt to write this object as .dbf.
ERROR:
invalid subscript type 'list'

> shp.AT[1]<-shp.tab # Try replacing the old Object[1] with my new table containing the new attribute.

> shp.AT # The table portion fo the shp.AT is gone. No attributes.
$dbf
[1] 134 279 399 428

$header
$header$file.version
[1] 3

$header$file.year
[1] 113

$header$file.month
[1] 4

$header$file.day
[1] 12

$header$num.records
[1] 4

>write.dbf(shp.AT, gsub(".shp", ".dbf", Shape)) # If I go ahead and overwrite anyway...

My attributes are gone and replaced with an attribute table that contains a single field "dataframe". I recurse the script to again read the attribute table.

> shp.tab
  dataframe
1       134
2       279
3       399
4       428

So, I think I'm close. Can anyone help me get this back into the shapefile attribute table? Or, is there a way better method?

Thanks

Answer

vitale232 picture vitale232 · Jun 22, 2013

I'm not sure I totally understand what you're trying to do. It looks like you just want to add a new column to the attribute table? If this is right, then just treat it like any dataframe.

library(rgdal)
dsn <- system.file("vectors", package = "rgdal")
shp<-readOGR(dsn = dsn, layer = 'cities')
shp$NewAT<-1:nrow(shp)

This works perfectly with a shapefile I have on my system. I typically rely on rgdal to read in my shapefiles, using the readOGR() function. I'm fairly certain the shapefile() function you were calling also calls rgdal.

Edited to add reproducable dataset.