add_neighbors: Add neighbors to adjacency information

In RSTr: Gibbs Samplers for Discrete Bayesian Spatiotemporal Models

Add neighbors to adjacency information

Description

Modifies adjacency to indicate that neighs they should be treated as neighbors.

Usage

add_neighbors(adjacency, neighs)

Arguments

adjacency	Adjacency information generated by spdep::poly2nb().
neighs	A vector of regions to mark as adjacent. Accepts a vector of indices or names assigned to adjacency.

Details

add_neighbors() is useful when adjacency information generated by spdep::poly2nb() indicates lone regions without links/neighbors, particularly in island counties such as the Hawaiian islands, Nantucket in Massachusetts, or San Juan in Washington. Note that add_neighbors() marks all listed counties as adjacent, so if you have a set of chaining counties where the first may not be connected to the last, several instances of add_neighbors() will be needed.

Value

A modified adjacency list.

Examples

if (requireNamespace("sf", quietly = TRUE) &&
    requireNamespace("spdep", quietly = TRUE)) {

  mamap <- sf::st_as_sf(mamap[order(mamap$GEOID), ])
  ma_adj <- spdep::poly2nb(mamap)
  new_neighs <- c(1, 4, 10) # attach regions 1, 4, and 10
  ma_adj <- add_neighbors(ma_adj, new_neighs)

  # Add neighbors by FIPS code instead of index
  ma_adj <- suppressWarnings(spdep::poly2nb(mamap))
  names(ma_adj) <- mamap$GEOID
  ma_adj <- add_neighbors(ma_adj, neighs = c("25001", "25007", "25019"))

  ma_adj <- suppressWarnings(spdep::poly2nb(mamap))
  ma_adj <- add_neighbors(ma_adj, c(1, 4)) # only attach 1 and 4
  ma_adj <- add_neighbors(ma_adj, c(4, 10)) # only attach 4 and 10
}

RSTr documentation built on Jan. 31, 2026, 9:07 a.m.