polygon object constructed from data frame breaks plot

[barryrowlingson]

> packageVersion("sf")
[1] ‘0.5.1’

Create a square:

> d = data.frame(x=c(0,1,1,0,0), y=c(0,0,1,1,0))
> d
  x y
1 0 0
2 1 0
3 1 1
4 0 1
5 0 0

Now try and make a polygon from the coordinates. First, as documented, converting d to a matrix:

> st_polygon(list(as.matrix(d)))
POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))

Secondly, without matrix conversion:

> st_polygon(list(d))
POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))

Both objects print the same, so my first assumption would have been that this has worked...

The first way plots correctly, but the second way errors:

> plot(st_polygon(list(as.matrix(d))))
> plot(st_polygon(list(d)))
Error in CPL_get_bbox(obj, 2) : 
  Not compatible with requested type: [type=list; target=double].

The structures are a bit different:

> str(st_polygon(list(d)))
List of 1
 $ :'data.frame':	5 obs. of  2 variables:
  ..$ x: num [1:5] 0 1 1 0 0
  ..$ y: num [1:5] 0 0 1 1 0
 - attr(*, "class")= chr [1:3] "XY" "POLYGON" "sfg"
> str(st_polygon(list(as.matrix(d))))
List of 1
 $ : num [1:5, 1:2] 0 1 1 0 0 0 0 1 1 0
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : NULL
  .. ..$ : chr [1:2] "x" "y"
 - attr(*, "class")= chr [1:3] "XY" "POLYGON" "sfg"

Not sure if the solution is to coerce data frames to matrix before manipulation, or erroring, or figuring out why plot fails...

[edzer]

This also works:

> st_multilinestring(list(matrix(letters[1:8],4)))
MULTILINESTRING ((a e, b f, c g, d h))

but won't plot for a similar reason. Do you also want to catch that?