I apologize for raising the same topic from time to time,
but each time I have to subset Spatial*DataFrame
objects (where * stands for polygons, lines or points) I
get some problems.
Last year Roger was kindly advising:
"Just think of Spatial*DataFrame objects as data.frame objects and things
will be much clearer"
Nevertheless, when I have to subset my lines now, I find that, given
> str(fl1,max.level=2)
Formal class 'SpatialLinesDataFrame' [package "sp"] with 4 slots
..@ data :'data.frame': 4 obs. of 2 variables:
..@ lines :List of 4
..@ bbox : num [1:2, 1:2] 448617 4630059 450088 4631874
.. ..- attr(*, "dimnames")=List of 2
..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
with
> f...@data
CodLin Comment
0 1 <NA>
1 2 <NA>
2 3 <NA>
3 4 <NA>
I can subset the data frame either as
> f...@data[1,]
CodLin Comment
0 1 <NA>
or as
> f...@data["0",]
CodLin Comment
0 1 <NA>
but for the SLDF, while I can use
> plot(fl1[1,])
I cannot use:
> plot(fl1["0",])
Error: trying to get slot "Lines" from an object of a basic class
("NULL") with no slots
So what would be the way of subsetting by IDs?
Also, Roger advised to get the IDs through either
> sapply(slot(fl1, "lines"), function(x) slot(x, "ID"))
[1] "0" "1" "2" "3"
or
> rownames(as.data.frame(fl1))
[1] "0" "1" "2" "3"
Considering that getting the IDs is an important task, would not
be appropriate having an specific function, as in the case of
coordinates()?
For example, ID(fl1) would be a lot easier to remember.
(I know I can do that function for my personal use, but then you end up
not using standard R)
Thanks!
Agus
begin:vcard
fn:Agustin Lobo
n:Lobo;Agustin
org:Institut de Ciencies de la Terra "Jaume Almera" CSIC
adr:;;Lluis Sole Sabris s/n;Barcelona;;08028;Spain
email;internet:agustin.l...@ija.csic.es
url:http://www.ija.csic.es/gt/obster
version:2.1
end:vcard
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