Why does dput()/dput2() not work with Polygons / SpatialPolygons

Question

I would like to ask another question, which includes SpatialPolygons. In order to make it reproducible I wanted to use dput() for the SpatialPolygons object, but its not outputting a reproducible structure.

Why can I use dput() with SpatialPoints, but not with Lines/SpatialLines, Polygons/SpatialPolygons?

Is the only workaround, to export the coordinates and recreate the SpatialPolygons in the example?

Test Data:

library(sp)
df = data.frame(lon=runif(10, 15,19), lat=runif(10,40,45))

dput(SpatialPoints(coordinates(df)))

dput(Lines(list(Line(coordinates(df))), 1))
dput(SpatialLines(list(Lines(list(Line(coordinates(df))), 1))))

dput(Polygons(list(Polygon(df)), 1))
dput(SpatialPolygons(list(Polygons(list(Polygon(df)), 1))))

dput(SpatialPolygons(list(Polygons(list(Polygon(df)), 1))), control="all")

The dupt2() method from this answer works for Lines/SpatialLines but not for Polygons/SpatialPolygons, where this error occurs:

Error in validityMethod(object) : object 'Polygons_validate_c' not found

So how to make a SpatialPolygons-object reproducible?

A workaround would be to convert the objects to simple features and then use dput(). They can obviously be deparsed.

Example using LINESTRING and POLYGON:

library(sp)
library(sf)
df = data.frame(lon=runif(10, 15,19), lat=runif(10,40,45))

SLi = SpatialLines(list(Lines(list(Line(coordinates(df))), 1)))
SPo = SpatialPolygons(list(Polygons(list(Polygon(df)), 1)))

dput(st_as_sf(SLi))
dput(st_as_sf(SPo))

please add library calls to your function, seems like you're using package sp — Moody_Mudskipper
dput(SpacialLines) works for me, however, with polygons I get the error Error in validityMethod(object) : object 'Polygons_validate_c' not found — Mako212
Library added. Yes the dput() method works, but the output wont be reproducible. It will incldue something like lines = list(<S4 object of class structure("Lines", package = "sp")>) — SeGa
from ?dput, Deparsing an object is difficult, and not always possible. With the default control, dput() attempts to deparse in a way that is readable, but for more complex or unusual objects (see dump), not likely to be parsed as identical to the original. — Moody_Mudskipper
and This is not a good way to transfer objects between R sessions. dump is better, but the function save is designed to be used for transporting R data, and will work with R objects that dput does not handle correctly as well as being much faster. So maybe use dump instead ? — Moody_Mudskipper

IRTFM IRTFM · Accepted Answer · 2018-07-26T19:57:09

After running the code I mentioned in the comments, I decided I would offer a tentative solution and see if you a) have the same results on your system, and b) whether it addressed the issues you were having.

 newSpPa <- dput(SpatialPolygons(list(Polygons(list(Polygon(df)), 1))), control="all")
 oldSpPa <- SpatialPolygons(list(Polygons(list(Polygon(df)), 1))) 
 identical(oldSpPa, newSpPa) 
#[1] TRUE

It wasn't clear from my reading your question whether the return of a call to new("SpatialPolygons", ...) was deemed to be unsatisfactory. I think the assignment step that I did was different than your code and it's possible that my assignment would only succeed in the setting of previously defined objects being in the workspace at the time of creation. If that's the case then I think the typical suggestion would be to do this in the setting of package-creation.

Why does dput()/dput2() not work with Polygons / SpatialPolygons

1 Answers