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polygon neighbor matrix

I second the `gTouches` suggestion. There's a ref here:
http://stackoverflow.com/a/26499134/1457051 but the gist of it is
(this user needed adjacent polygons in ghana):

library(rgeos)
library(rgdal)

# using http://data.biogeo.ucdavis.edu/data/diva/adm/GHA_adm.zip
ghana <- readOGR("GHA_adm", "GHA_adm1")

gTouches(ghana, byid=TRUE)

##       0     1     2     3     4     5     6     7     8     9
## 0 FALSE  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE
## 1  TRUE FALSE FALSE  TRUE FALSE  TRUE FALSE FALSE  TRUE  TRUE
## 2  TRUE FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE  TRUE
## 3  TRUE  TRUE  TRUE FALSE  TRUE FALSE FALSE FALSE  TRUE FALSE
## 4 FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE  TRUE FALSE
## 5 FALSE  TRUE FALSE FALSE FALSE FALSE  TRUE  TRUE  TRUE FALSE
## 6 FALSE FALSE FALSE FALSE FALSE  TRUE FALSE  TRUE FALSE FALSE
## 7 FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE
## 8 FALSE  TRUE FALSE  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE
## 9  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
On Mon, Aug 31, 2015 at 2:19 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote: