Save layers from a gdb as sf objects in a loop

Question

I'm taking an R class and I have an assignment that I'm trying to figure out. Instructor wants us to save all layers in a gdb file as sf objects. He told us that we should use loops.

I'm able to import the gdb file using

scd <- st_read(dsn='/path/to.gdb')

And I'm also able to list layers using

scdl <- st_layers(dsn='/path/to.gdb')

Update:

  
  st_read(dsn = '/path/to.gdb', layer=i)
  feat <- st_read(code here)
}

i

this is what I have done so far which loops over the layernames. but when I try to assign them to objects using feat <- st_read(code here) line, it breaks my loop.

"Error in CPL_read_ogr(dsn, layer, query, as.character(options), quiet, : Expecting a single value: [extent=5]. In addition: Warning message: In if (nchar(dsn) < 1) { : the condition has length > 1 and only the first element will be used"

Answer 1

In the following code the sf objects are read and added to a list, which is a safe way of reading things in a for loop.

library(sf)
layer_list = st_layers("to.gdb")

layers_sf = list()
for(i in 1:length(layer_list$name)) {
  layers_sf[[layer_list$name[i]]] = read_sf(dsn = "to.gdb", layer = layer_list$name[i])
}
 # a plot f the first to test the list object `layers_sf`:
plot(layers_sf[[1]])

Answer 2

I had my class and this is what I was able to come up with, which worked and got accepted;

scdl <- st_layers('path/to.gdb')

for(i in scdl$name) {
  
  feat <- st_read(dsn = 'path/to.gdb', layer=i)
  plot(feat)
}

My professor said function lapply would have been the best solution but this works as well. Thank you for all the help and suggestions, much appreciated!

Answer 3

Replace the for-loop with the purrr package.

st_layers will list all of the names within your gdb and then purrr::map uses the list of names with st_read to read each vector into R from your gdb.

library(sf)
path<-"path/to/your.gdb"
gdb<-st_layers(path)
list_of_features<-purrr::map(gdb$name,~st_read(dsn=path,layer=.))