Convert an igraph graph to the CSR representation used by the kernels

The composable building blocks [lcda_construct()], [lcda_repair()], and [lcda_local_search()] operate on a compressed-sparse-row (CSR) view of the graph rather than on the igraph object directly. `as_csr()` builds that view: an undirected simple graph becomes a list of `indptr`/`indices`/`weights` (0-based, as the C++ kernels expect) together with the originating igraph. A numeric `weight` edge attribute, if present, is carried through (the kernels reduce exactly to the unweighted case when all weights are 1).

Usage

as_csr(graph)

Arguments

graph

an undirected [igraph::igraph] object. Multi-edges are collapsed to a simple graph; directed graphs are not supported.

Value

a CSR list with elements `n`, `indptr`, `indices`, `weights`, and `igraph`, suitable as the `csr` argument of [lcda_construct()], [lcda_repair()], and [lcda_local_search()].

Examples

g <- igraph::make_graph("Zachary")
csr <- as_csr(g)
str(csr[c("n", "indptr", "indices")])
#> List of 3
#>  $ n      : num 34
#>  $ indptr : int [1:35] 0 16 25 35 41 44 48 52 56 61 ...
#>  $ indices: int [1:156] 1 2 3 4 5 6 7 8 10 11 ...