How can I eliminate some areas by attribute from a shapefile in R and create a new shapefile?

Question

I have been at this for a while now and have had some success, however when it comes to rewriting the file, I have had none. The shapefile I am working with is a polygon shapefile of metro and micropolitan areas but I am not interested in the micropolitan areas so I am working with the shp in R to try and eliminate them from my map. Data Source To download the right file, make sure that you select "All States in one national file" under "Metropolitan/Micropolitan Statistical Area (2010)" Here's what I have so far: ``` library(maptools) met=readShapeSpatial("tl_2010_us_cbsa10.shp") met=met@data ``` Before subset: ``` NAMELSAD10 LSAD10 Anchorage, AK Metro Area - M1 Clarksdale, MS Micro Area - M2 Richmond, VA Metro Area - M1 Big Spring, TX Micro Area - M2 Dallas-Fort Worth-Arlington, TX Metro Area - M1 Rio Grande City-Roma, TX Micro Area - M2 ``` then: ``` submet=subset(met, LSAD10 == "M1") ``` After subset: ``` NAMELSAD10 LSAD10 Anchorage, AK Metro Area - M1 Richmond, VA Metro Area - M1…

Accepted Answer

When you do `met=met@data` you are losing the Spatial aspect of `met` and just getting the plain old data frame.

Then you subset that data frame okay, and then you try and `writeSpatialShape` it. Whoa. The `submet` object doesn't have any polygons or coordinates. `writeSpatialShape` should barf. But it manages to swallow it whole and keep it down. Check this out:

```
> writeSpatialShape(1,"foo.shp")
> 
```

and as you observed, no shapefile is created. Wow, that's pretty sucky error handling.

Two solutions: 1, work on the actual object rather than the data component, like this:

```
met = readOGR(dir,name)
submet = met[met$thing=="whatever",]
writeOGR(submet,dir,newname,"ESRI Shapefile")
```

2, use `package:rgdal` and `read/write|OGR` which not only handles projections but is violently sick if you try and make it eat something unpalatable:

```
> writeOGR(1,".","foo","ESRI Shapefile")
Error: inherits(obj, "Spatial") is not TRUE
```

How can I eliminate some areas by attribute from a shapefile in R and create a new shapefile?

Solution

Problem