[R-sig-Geo] Combine two polygons

[Miluji Sb]

Thank you for your replies. I think I am misunderstanding something. I have
read the shapefile using sf. I would like to combine polygons for Cyprus
and Northern Cyprus only within the world shapefile and keep all the other
polygons as they are.

world <- sf::st_read(dsn = "~/gadm36_levels_shp", layer = "gadm36_0")

Is something like the following correct? I was thinking of generating a
group variable which is unique to all the countries except Cyprus and
Northern Cyprus. I a probably making this too complicated.

world %>%
  group_by(group) %>%
  summarise(geometry = sf::st_union(geometry)) %>%
  ungroup()

Thank you again.

Best regards,

Milu

On Fri, Apr 28, 2023 at 8:56 AM Roger Bivand <Roger.Bivand using nhh.no> wrote:

> On Fri, 28 Apr 2023, Michael Sumner wrote:
>
> > fwiw, a method with geodata/terra
> >
> > cyp <- geodata::gadm(country = c("CYP", "XNC"), path = tempdir(),
> version =
> > "3.6")
> >
> > terra::aggregate(cyp)
> >
>
> and as per
> https://github.com/r-spatial/evolution/blob/main/pkgapi_230305_refs.csv.
>
> > see ?terra::writeVector to write it out
> >
> > (rgdal is very old and you should abandon it, it will be removed from
> > support by the end of this year)
>
> Thank you! Yes, sp will by default switch to using sf in place of rgdal
> for creating "CRS" objects, and under sp::spTransform in June, and all
> three retiring packages rgdal, rgeos, and maptools will be gone by October
> 2023. An sp release will appear in May with a transition guide.
>
> It seems that terra does not have an object corresponding to sp's "CRS" or
> sf's "crs". As far as I can see, one needs to create an empty
> SpatVector/SpatRaster object and assign a CRS, coerce to "Spatial", and
> extract its slot. If this makes sense, sp could use terra (and
> raster, needed for coercion) rather than sf where workflows did not
> otherwise use sf. Very grateful for input here or
> https://github.com/r-spatial/evolution/issues.
>
> Roger
>
> >
> >
> > (just as an aside, we can't hit the geodata vector urls directly with
> gdal
> > as we can with the rasters, as they are in an R specific format)
> >
> > Cheers, Mike
> >
> >
> > On Fri, Apr 28, 2023 at 10:52 AM Ben Tupper <btupper using bigelow.org> wrote:
> >
> >> Hi,
> >>
> >> You might try st_union() from the sf package
> >> https://r-spatial.github.io/sf/articles/sf3.html#geometrical-operations
> >>
> >>
> >>
> >> On Thu, Apr 27, 2023 at 5:37 PM Miluji Sb <milujisb using gmail.com> wrote:
> >>
> >>> Dear all,
> >>>
> >>> I am using the country-level shapefile from GADM. I would like to merge
> >>> Cyprus and North Cyprus into one polygon. Is this possible? I am using
> >>> rgdal to read the shapefile, subset, and then rewrite it. Any help will
> >> be
> >>> highly appreciated.
> >>>
> >>> ##
> >>> world <- readOGR("~/gadm36_levels_shp", layer = "gadm36_0")
> >>>
> >>> Best regards,
> >>>
> >>> Milu
> >>>
> >>>         [[alternative HTML version deleted]]
> >>>
> >>> _______________________________________________
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> >>> R-sig-Geo using r-project.org
> >>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >>>
> >>
> >>         [[alternative HTML version deleted]]
> >>
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> >>
> >
> >
> >
>
> --
> Roger Bivand
> Emeritus Professor
> Department of Economics, Norwegian School of Economics,
> Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
> e-mail: Roger.Bivand using nhh.no
> https://orcid.org/0000-0003-2392-6140
> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
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