Creates a list of connected nodes following the graph representation of a spatial connectivity matrix.
edges(C, unique_pairs_only = TRUE)
A connectivity matrix where connection between two nodes is indicated by non-zero entries.
By default, only unique pairs of nodes (i, j) will be included in the output.
Returns a data.frame
with three columns. The first two columns (node1
and node2
) contain the indices of connected pairs of nodes; only unique pairs of nodes are included (unless unique_pairs_only = FALSE
). The third column (weight
) contains the corresponding matrix element, C[node1, node2]
.
This is used internally for stan_icar
and it is also helpful for creating the scaling factor for BYM2 models fit with stan_icar
.