在R中使用shapefile显示区域的子集

Question

I have a shapefile of the UK: https://geoportal.statistics.gov.uk/Docs/Boundaries/Local_authority_district_(GB)_2014_Boundaries_(Generalised_Clipped).zip

I've read the shapefile into a variable, UK

>UK <- readOGR(dsn = "....."
>England <- UK

I'd like to only display English Local Authority regions. They are specified in the LAD_DEC_2014_GB_BGC.dbf where LAD14CD starts with "E"

>UK@data

      LAD14CD                      LAD14NM                 LAD14NMW

0   E06000001                   Hartlepool                     <NA>
1   E06000002                Middlesbrough                     <NA>
2   E06000003         Redcar and Cleveland                     <NA>
371 W06000015                      Cardiff                 Caerdydd

>#filter UK@data and replace England@data with only English regions
>England@data <- UK@data$LAD14CD[c(grep("^E", UK$LAD14CD))]

>plot(England)

But the grep command appears to change the shapefile into a factor, meaning the plot looks like this:

Answer 1

With this command:

England <- UK@data$LAD14CD[c(grep("^E", UK$LAD14CD))]

...you are subsetting just one column from the data slot, not the whole shapefile and assigning that to England .

This ought to do the job:

England <- UK[grep("^E", UK@data$LAD14CD),]

Note, you need the trailing comma in there! Also you don't need to wrap the grep statement in c() , but that doesn't hurt it's just unnecessary.

Answer 2

I ended up using dplyr and grepl instead to make things simpler:

library('rgdal')
library('dplyr')

UK <- readOGR(dsn="LAD_DEC_2014_GB_BGC.shp", layer="LAD_DEC_2014_GB_BGC") %>%
  subset(grepl("^E", LAD14CD))
plot(UK)