How to create and empty SpatialLinesDataFrame in R

Question

I need to create and SpatialLinesDataFrame with a predefined structure (9 fields). I'm performing a function over a list of shp which I want to append to this empty spatiallinesdataframe.

I already know how to save each shp within a folder and then merge all, but now, I'd like to merge all the sph within the iteration to avoid save and reread steps.

Answer 1

I'd use this trick, which is to create a 1-row SLDF with the right attributes, and then drop the first and only row, leaving you with nothing:

> library(sp)
> library(raster)

Here's the beef:

> s = SpatialLinesDataFrame(
 sl=SpatialLines(
 LinesList=list(
 Lines(
 list(
 Line(
 coords=matrix(c(0,1,0,1),2,2)
 )
 ),ID=1)
 )
 ),
 data=data.frame(a=1,b=2,c=3))[-1,]

Set up a one-line data frame with your attributes in the last line - here I've got three. The finale [-1,] drops the one row created, leaving you with:

> s
class : SpatialLinesDataFrame 
features : 0 
coord. ref. : NA 
variables : 3
names : a, b, c 

A SLDF with no rows (features) and 3 variables.

• César Arquero Cabral: This is exactly what I was looking for. Thanks a lot ¡