[R-sig-Geo] nb object in spdep from categorical attribute

[Dexter Locke]

Thanks so much.

The nb2blocknb(), aggregate.nb(), and union.nb() are fantastic functions!
Between these three functions I that I had not seen before I can accomplish
what I am seeking. It looks like the new spdep vignette has been greatly
expanded, which is also fantastic.

Thanks again,
Dexter


On Wed, Jun 20, 2018 at 8:24 AM Roger Bivand <Roger.Bivand using nhh.no> wrote:

> On Tue, 19 Jun 2018, Dexter Locke wrote:
>
> > Dear list,
> >
> > Does anyone know how to make nb objects (to eventually make spatial
> > weights) with spdep using an attribute in a shapefile's data frame?
> >
> > Consider, for example, all property parcels on the same street segment
> > should be defined as neighbors. In the parcel polygons I have the
> > associated street segment name.
> >
> > KNN forces sparsely settled areas to become neighbors, which is
> undesirable
> > for the subsequent analyses.
> >
> > Distances between parcels vary, so distance-based neighbors are also
> > undesirable in this case.
> >
> > Contiguity-based methods do not connect parcels on opposite sites of the
> > same street segment.
> >
> > Is there a way to use an attribute to define what constitutes a neighbor?
>
> Yes, spdep::nb2blocknb() is a specific case where say observations without
> positional data are known to belong to an aggregate entity for which we
> have positional data. The output is an nb object with diagonal blocks (if
> the observations are sorted by block ID, not in the case below), as this
> example shows. You'll need the development version to run it, as released
> spdep::aggregate.nb() failed with empty aggregate sets - the nc median
> poish grid has such empty sets:
>
> # devtools::install.github("r-spatial/spdep")
> library(spdep)
> data(nc.sids)
> ncCC89.nb[sapply(ncCC89.nb, length) == 0L] <- 0L
> image(as(nb2listw(ncCC89.nb, zero.policy=TRUE), "CsparseMatrix"))
> anb <- aggregate(ncCC89.nb, interaction(nc.sids$M.id, nc.sids$L.id))
> image(as(nb2listw(anb, style="B"), "CsparseMatrix"))
> # when the neighbour object is not empty
> bnb <- nb2blocknb(anb, as.character(interaction(nc.sids$M.id,
>    nc.sids$L.id)))
> image(as(nb2listw(bnb, style="B"), "CsparseMatrix"))
> # and when the neighbour object is empty
> anb1 <- lapply(anb, function(x) x <- 0L)
> attributes(anb1) <- attributes(anb)
> bnb1 <- nb2blocknb(anb1, as.character(interaction(nc.sids$M.id,
>    nc.sids$L.id)))
> image(as(nb2listw(bnb1, style="B"), "CsparseMatrix"))
>
> This isn't your case, but crafting an nb object by hand (adding
> attributes after creating the list) then using spdep::union.nb or similar
> to combine with a positional nb (such as poly2nb) may work. For parcels
> across a stream or street, maybe look at the snap= argument if the streets
> are narrower than frontages. Could you provide a small reproducible
> example?
>
> Hope this clarifies,
>
> Roger
>
> >
> > All ideas welcome,
> > Dexter
> >
> >       [[alternative HTML version deleted]]
> >
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> >
>
> --
> Roger Bivand
> Department of Economics, Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; e-mail: Roger.Bivand using nhh.no
> http://orcid.org/0000-0003-2392-6140
> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
>

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