Splitting MultiPolygon shapefile into separate Polygons in R

Question

I have a polygon shapefile with 2 features. I want to split the MultiPolygon shp into separate shapefiles based on a column of the attribute table. What I've tried so far is this code based on that answer but without success:

all_shp = readOGR("mydir", layer = "test")

#extract features to a new polygon
shp1 = all_shp[1,]
writeOGR(shp1, dsn = "mydir", layer = "shp1",
         driver = "ESRI Shapefile" )


#create function
extract_shp = function(all_shp){
  #iterate through the feature class
  for(i in 1:nrow(all_shp)) { p <- all_shp[i,] }
  #extract features to a new polygon
  shp1 = p
  
}

I am pasting the data using the dput command:

 test = new(
      "SpatialPolygonsDataFrame",
      data = structure(
        list(
          id = c(14985,
                 23552),
          left = c(2665569.79702, 2670699.79702),
          top = c(1412205.45671,
                  1407615.45671),
          right = c(2665839.79702, 2670969.79702),
          bottom = c(1411935.45671,
                     1407345.45671),
          id_sample = c(1L, 1L)
        ),
        class = "data.frame",
        row.names = 0:1
      ),
      polygons = list(
        new(
          "Polygons",
          Polygons = list(
            new(
              "Polygon",
              labpt = c(80.3367355387047, 16.2821390031233),
              area = 6.1440311016086e-06,
              hole = FALSE,
              ringDir = 1L,
              coords = structure(
                c(
                  80.3354759967946,
                  80.3379981575006,
                  80.3379950690668,
                  80.3354729314431,
                  80.3354759967946,
                  16.2833585003835,
                  16.2833555285503,
                  16.2809195021546,
                  16.2809224739735,
                  16.2833585003835
                ),
                .Dim = c(5L,
                         2L)
              )
            )
          ),
          plotOrder = 1L,
          labpt = c(80.3367355387047, 16.2821390031233),
          ID = "0",
          area = 6.1440311016086e-06
        ),
        new(
          "Polygons",
          Polygons = list(
            new(
              "Polygon",
              labpt = c(80.3523654989901,
                        16.2402853833502),
              area = 6.1434245505222e-06,
              hole = FALSE,
              ringDir = 1L,
              coords = structure(
                c(
                  80.3511062267076,
                  80.3536279907441,
                  80.353624759728,
                  80.3511030187666,
                  80.3511062267076,
                  16.2415050209594,
                  16.2415019107378,
                  16.2390657420334,
                  16.2390688522397,
                  16.2415050209594
                ),
                .Dim = c(5L, 2L)
              )
            )
          ),
          plotOrder = 1L,
          labpt = c(80.3523654989901,
                    16.2402853833502),
          ID = "1",
          area = 6.1434245505222e-06
        )
      ),
      plotOrder = 1:2,
      bbox = structure(
        c(
          80.3354729314431,
          16.2390657420334,
          80.3536279907441,
          16.2833585003835
        ),
        .Dim = c(2L, 2L),
        .Dimnames = list(c("x", "y"), c("min", "max"))
      ),
      proj4string = new("CRS",
                        projargs = "+proj=longlat +datum=WGS84 +no_defs")
    )

I am using RStudio 1.4.1717, R 4.1.1 and Windows10 x64

Answer 1

I found the solution based on this post. The code is:

library(sp)
library(rgdal)

#read shp
singlepoly = readOGR("C:/Users/Geography/Desktop/test_cnn", layer = "samples1_exchange")
#get the names of the attribute table
names(singlepoly)

#select the column of the attribute table that will determine the split of the shp
unique <- unique(singlepoly$id)

#create new polygons based on the determined column
for (i in 1:length(unique)) {
  tmp <- singlepoly[singlepoly$id == unique[i], ]
  writeOGR(tmp, dsn=getwd(), unique[i], driver="ESRI Shapefile",
           overwrite_layer=TRUE)
}