Remove Edges from an Adjacency List

Remove one or more undirected edges from an adjacency list and return the modified list.

subtract_edge(adj, v1, v2, ids = NULL, zero = TRUE)

Arguments

adj

List of neighbors, one entry per vertex.

v1

vector of vertex identifiers for the first vertex. Can be an integer index or a value to look up in ids, if that argument is provided. If more than one identifier is present, disconnects each to corresponding entry in v2, if an edge exists.

v2

vector of vertex identifiers for the second vertex. Can be an integer index or a value to look up in ids, if that argument is provided. If more than one identifier is present, disconnects each to corresponding entry in v2, if an edge exists.

ids

Optional identifier vector used to look up row indices. If provided, each entry in v1 and v2 must match exactly one entry.

zero

Logical. TRUE when the adjacency list stores zero-based neighbor indices and FALSE when it stores one-based indices.

Value

Adjacency list with the requested edges removed symmetrically.

Examples

data(towns)
adj <- adjacency(towns)

subtract_edge(adj, 2, 3)
#> [[1]]
#> [1] 3 4 6
#> 
#> [[2]]
#> [1] 4
#> 
#> [[3]]
#> [1] 3 5
#> 
#> [[4]]
#> [1] 0 4 2 6 5
#> 
#> [[5]]
#> [1] 0 1 3 5
#> 
#> [[6]]
#> [1] 3 4 2 6
#> 
#> [[7]]
#> [1] 0 3 5
#> 
subtract_edge(adj, "West Haverstraw", "Stony Point", towns$MUNI)
#> [[1]]
#> [1] 3 4 6
#> 
#> [[2]]
#> [1] 4
#> 
#> [[3]]
#> [1] 3 5
#> 
#> [[4]]
#> [1] 0 4 2 6
#> 
#> [[5]]
#> [1] 0 1 3 5
#> 
#> [[6]]
#> [1] 4 2 6
#> 
#> [[7]]
#> [1] 0 3 5
#>