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I have several polygon shapefiles that I need to merge into one using a loop in R. I want to start with an empty shapefile and merge it with the existing shapefiles. All shapefiles will be chacked before the merge that they have the same fields.

I can think of two options:

  1. create an empty shapefile in ArcMap and read it into R. I tried this with readOGR and got an error:
library(rgdal)
EI_GIS_ALL = readOGR(dsn = EI_GIS_ALL_dsn, layer=EI_GIS_ALL_FileName)
Error in readOGR(dsn = EI_GIS_ALL_dsn, layer = EI_GIS_ALL_FileName) : 
  no features found
  1. Create an empty shapefile in R and use union to merge it with existing shapefiles. The union is like in maycca's solution in Merging multiple SpatialPolygonDataFrames into 1 SPDF in R?

Any suggestions?

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  • Spacedman nailed it but, I would add that you can avoid unique row.name issues by using sf and then coercing to sp. First create names vector shp <- list.files(getwd(), "shp$") then read in data s <- lapply(shp, function(x) sf::st_read(x) ) finally, merge and coerce to sp s <- as(do.call(rbind, s), "Spatial") With large data you will also get better read times. – Jeffrey Evans Oct 27 '20 at 22:26
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Probably easier to use another pattern, eg special treatment of the first item:

first=TRUE
for(shp in shapefiles){
   # this function reads in a shapefile from shp and returns sp object:
   shpdata = read_in_and_check(shp)
   if(first){
      output=shpdata
      first=FALSE
   } else {
      output=bind(output, shpdata)
   }
}

or get your shapes into a list and use do.call with bind:

# shpdatas becomes a list of sp-class objects:
shpdatas = lapply(shapefiles, read_in_and_check)
output = do.call(bind, shpdatas)
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  • Perfect! Thanks – Ilik Oct 27 '20 at 20:22

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