Merging two spatial objects in R: spCbind gives error "row names not identical"

Question

I have two SpatialPolygonsDataFrames. One is the LSOA shapefile of Great Britain (i.e., Great Britain divided into ~41,000 regions with approximately equal population densities), the other is a bunch of regions in Great Britain (coal fields). I want to add the coal field info to the LSOA object, in order to have a variable added to the LSOA object that tells me whether an LSOA region falls into a coal field or not.

I got the shapefiles from here:

• LSOA regions: https://www.statistics.digitalresources.jisc.ac.uk/dataset/2011-census-geography-boundaries-lower-layer-super-output-areas-and-data-zones/resource-1
• Coal mines: https://data.gov.uk/dataset/coal-mining-reporting-area

This is how I attempted to do the merge:

# read in LSOA regions
LSOA <- readOGR(dsn = "Infuse", layer = "infuse_lsoa_lyr_2011")
# transform map to OSGB projection
bng = '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs'
LSOA.bng <- spTransform(LSOA,bng)

# read in coalmining regions:
coalmine <- readOGR(dsn = "coalmining_shapefiles", layer = "Coalfield_polygon")
# transform map to OSGB projection
coalmine.bng <- spTransform(coalmine,bng)

# merge data
coalmines.LSOA.over <- over(LSOA.bng, coalmine.bng)
LSOA.coalmines <- spCbind(LSOA.bng,coalmines.LSOA.over)

This is the error message I get after the spCbind command:

Error in spCbind(LSOA.bng, coalmines.LSOA.over) : row names not identical

What did I do wrong?

Answer 1

As the output of sp::over is ordered to the input, you don't need to join/merge the two objects; you only need to add the targeted (or desired) columns from the output of over to your data frame.

Using base r, you define a new variable of your data frame with the $ operator, then you assign the output of over to it:

lsoa.bng$var <- coalmines.lsoa.over$your_target_variable

if it doesn't match a name already in your df, you may also cbind it:

lsoa.bng <- cbind(lsoa.bng, coalmines.lsoa.over$your_target_variable)