How to use rbind with SPDFs when the number of columns of arguments do not match?

Question

I'm looking to use rbind to combine the SPDFs of different European countries. However, I'm looking to use SPDFs of different levels of regions. Unfortunately, I'm getting the following error:

library(sp)
library(raster)

France_map <- getData(name = "GADM", country = "FRA", level = 0)
Germany_map <- getData(name = "GADM", country = "DEU", level = 1)
Belgium_map <- getData(name = "GADM", country = "BEL", level = 2)

test <- rbind(France_map, Germany_map, Belgium_map, makeUniqueIDs = TRUE)

Error in rbind(deparse.level, ...) : 
  numbers of columns of arguments do not match

How do I need to treat the individual SPDFs so that they can be bound together?

Answer 1

The attributes/columns in each dataframe are completely different, but if you want to bind with rbind they need to match.

Is there a reason for the different administrative levels? If you were to use (e.g.) level=1 for each country, the attributes would match and the rbind will work as intended.

If you need to keep the specified levels, then you'll need to reduce and harmonise the attributes/columns before attempting the rbind.

Answer 2

There is no actual need for a two-step approach when trying to combine the single objects in such a way that all columns are kept (ie. missing columns are filled with NA). In fact, this can be achieved in one go using bind() from raster:

out1 = bind(France_map, Germany_map, Belgium_map)

# or, when dealing with lists (eg. resulting from some *apply call),
countries = list(France_map, Germany_map, Belgium_map)
out2 = do.call(bind, countries)