Producing a conditional adjacency matrix

Thank you so much Roger! Works like a charm.

Rhys

Hi Roger,

Including a bit more detail below (my apologies if this is just complete gibberish ? first time posting to a forum like this):

First, I add a random ID variable to the columbus dataset indicating the variable I?d like to base my exclusions on in the final neighbor list:
columbus$ID <- sample(1:3, nrow(columbus), replace=T)

In my case, that produced the following IDs for the first 4 polyids:

POLYID 1: 3
POLYID 2: 2
POLYID 3: 3
POLYID 4: 1

Second, col.ga.nb indicates that each of the previous POLYID?s has the following neighbors

View(col.gal.nb)

POLYID 1 (w new assigned ID of 3): 2, 3
POLYID 2 (? ? 2): 1, 3, 4
POLYID 3 (? ? 3): 1, 2, 4, 5
POLYID 4 (? ? 1): 2, 3, 5, 8

Third (or brevity?s sake) looking only at POLYID 1 (with new ID = 3):

Its neighbors from col.ga.nb (POLYID 2 and 3) have ID values of 3 and 1 respectively

My end goal would be to produce a new list in which POLYID 1?s only neighbor is POLYID 3 (with an ID of 1). POLYID 2 would be excluded, as its ID value matches its parent.

Leave col.gal.nb as it is, and generate a list of general weights:

library(spdep)
Loading required package: sp
Loading required package: spData
Loading required package: sf
Linking to GEOS 3.7.2, GDAL 3.0.1, PROJ 6.2.0
data(columbus, package="spData")
ls()
[1] "bbs"        "col.gal.nb" "columbus"   "coords"     "polys"
col.gal.nb[[1]]
[1] 2 3
set.seed(1)
columbus$ID <- sample(1:3, nrow(columbus), replace=T)
columbus$ID[1]
[1] 1
columbus$ID[col.gal.nb[[1]]]
[1] 3 1 # second entry equal
glist <- lapply(seq(along=col.gal.nb), function(i)
 as.integer(columbus$ID[i] != columbus$ID[col.gal.nb[[i]]]))
glist[[1]]
[1] 1 0 # second weight zero