Using R, why am I unable to select a column from an sp Spatial Lines Dataframe?

Question

With utm_RDS being the spatial lines in question, derived from the following shapefile:

library(rgdal)
library(sp)
    RDSYS <- readOGR(dsn = "C:/************")

        utm_RDS <- spTransform(RDSYS, CRS("+proj=utm +zone=14 +datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0"))

We can then see

    > class(utm_RDS)
[1] "SpatialLinesDataFrame"
attr(,"package")
[1] "sp"

> head(utm_RDS)
An object of class "SpatialLinesDataFrame"
Slot "data":
   ID   NAME TYPE 
0 ******  <NA> <NA>      
1 ******  ***   ST      
2 ******  <NA> <NA>      
3 ******  <NA> <NA>      
4 ******  <NA> <NA>    

Among some omitted columns.

I am now interested in being able to select lines to plot and analyze given their type, but always seem to be met with error. For example,

utm_RDS@lines[utm_RDS$TYPE == "HWY"]
length(utm_RDS@lines[utm_RDS$TYPE == "HWY"])

[1] 46925

Which gives me the number of distinct lines in the shapefile.

But,

plot((utm_RDS@lines[utm_RDS$TYPE == "HWY"])) will not work, returns:

Error in xy.coords(x, y, xlabel, ylabel, log) : 
  'x' is a list, but does not have components 'x' and 'y'

and is of class "list".

Further,

> plot((utm_RDS[utm_RDS$TYPE == "HWY"]))
Error in `[.data.frame`(x@data, i, j, ..., drop = FALSE) : 
  undefined columns selected

Does anyone have a workaround for this?

Answer 1

Spatial*DataFrame objects inherit methods from dataframes, so your last attempt was almost correct; it's just missing a coma to indicate that you are filtering rows. It should be:

plot(utm_RDS[utm_RDS$TYPE == "HWY",])