Change Lines'IDs within a SpatialLines object

Thank you very much Roger, it is really helpful.

I had no idea SpatialLines (or SpatialPolygons) objects could be
manipulated this way. If I may ask, to which extent these objects can
be treated as data frames (I understand they are not?)? I may have
missed it but I haven't seen such thing in the documentation.

Incidentally I think your answer made me understand what
SpatialLinesDataFrame are (I used to think it was a different way to
store the shape's geometry but it is more about linking
attributes/variables to shapes ID's if I am correct).  It will serve
my purpose quite aptly.

Thanks a lot again, I already had more answers than I asked for.

Best regards,
Bastien

2015-12-09 17:40 GMT+01:00 Roger Bivand <Roger.Bivand at nhh.no>:

On Wed, 9 Dec 2015, Bastien Tran wrote:

Dear all,

I intend to make "copies" of SpatialLines object meaning I would like
to get the same geometry but with different IDs for the Lines.

Please use row.names(), so here:

row.names(L1) <- c("c", "d")

If L1 was a SpatialLinesDataFrame, the row.names of the data slot would also
be updated.

Roger

For instance using L1 from the SpatialLines example I would like to go
from:

str(L1)

Formal class 'SpatialLines' [package "sp"] with 3 slots
 ..@ lines      :List of 2
 .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
 .. .. .. ..@ Lines:List of 1
 .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
 .. .. .. .. .. .. ..@ coords: num [1:3, 1:2] 1 2 3 3 2 2
 .. .. .. ..@ ID   : chr "a"
 .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
 .. .. .. ..@ Lines:List of 1
 .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
 .. .. .. .. .. .. ..@ coords: num [1:3, 1:2] 1 2 3 3 1.5 1
 .. .. .. ..@ ID   : chr "b"
 ..@ bbox       : num [1:2, 1:2] 1 1 3 3
 .. ..- attr(*, "dimnames")=List of 2
 .. .. ..$ : chr [1:2] "x" "y"
 .. .. ..$ : chr [1:2] "min" "max"
 ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
 .. .. ..@ projargs: chr NA

to

str(L1)

Formal class 'SpatialLines' [package "sp"] with 3 slots
 ..@ lines      :List of 2
 .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
 .. .. .. ..@ Lines:List of 1
 .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
 .. .. .. .. .. .. ..@ coords: num [1:3, 1:2] 1 2 3 3 2 2
 .. .. .. ..@ ID   : chr "c"
 .. ..$ :Formal class 'Lines' [package "sp"] with 2 slots
 .. .. .. ..@ Lines:List of 1
 .. .. .. .. ..$ :Formal class 'Line' [package "sp"] with 1 slot
 .. .. .. .. .. .. ..@ coords: num [1:3, 1:2] 1 2 3 3 1.5 1
 .. .. .. ..@ ID   : chr "d"
 ..@ bbox       : num [1:2, 1:2] 1 1 3 3
 .. ..- attr(*, "dimnames")=List of 2
 .. .. ..$ : chr [1:2] "x" "y"
 .. .. ..$ : chr [1:2] "min" "max"
 ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
 .. .. ..@ projargs: chr NA


Is there a way to do so without rebuilding the SpatialLine object with
updated Lines objects (same Lines new IDs)? I assume it is possible to
update each ID slot directly in L1 somehow.

I expected something like

sapply(slot(L1, "lines"), function(x) assign(slot(x, "ID"),
paste0("copyof",slot(x, "ID")))

to do so but I am certainly missing something about assignments in S4
objects.

Thank you for any help.

Best regards,

Bastien Tran

--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no